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Different Forms of EnergyChapter 3
Kinds of Energybull Gravitational Potential Energy due to positionbull Kinetic Energy due to motionbull Heat Energy due to movement of heat energy
from regions of high energy to areas of low energy
bull Radiant Energy due to lightbull Chemical Potential Energy due to bondsbull Elastic Energy stressed objects that return to
their original shapebull Electrical Energy due to movement of electronsbull Nuclear Energy due to atomic fissionfusion
Kinetic Energy
bull Kinetic Energy is the energy an object has due to its motion
bull The KE depends on the mass and the speed
bull Ek or KE= frac12 mv2 bull E is Energy in Joules Jbull m is mass in kg v is velocity in ms
Example
bull What is the KE of a 6 kg curling stone moving at 4 ms
bull KE = frac12 mv2
bull = frac12 x 6kg x (4 ms)2
bull = frac12 x 6 x 16bull = 48 J
Activity
What is the Kinetic Energy of a 5 kg ball travelling horizontally at a speed of 10 ms
Exam QuestionA go lf ball is d ropped o u t o f a w indow w hich is 10 m above the grou nd T he ball has a m ass o f 50 g D isregard the effec ts o f a ir resis tan ce
10 m
W hat is the k inetic en ergy o f the b all just before it h its the ground
A )
10 J
B )
7 5 J
C )
5 0 J
D )
2 5 J
Potential Energybull If we lift up an object against gravity it now
has the ability to move it has the potential to fall down and use up the energy we put into it
bull Ep PE = mgh unit is Joules Jbull m is the mass in kgbull g is the acceleration due to gravity 981ms2
bull h is the height above the Earthrsquos surface m
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Kinds of Energybull Gravitational Potential Energy due to positionbull Kinetic Energy due to motionbull Heat Energy due to movement of heat energy
from regions of high energy to areas of low energy
bull Radiant Energy due to lightbull Chemical Potential Energy due to bondsbull Elastic Energy stressed objects that return to
their original shapebull Electrical Energy due to movement of electronsbull Nuclear Energy due to atomic fissionfusion
Kinetic Energy
bull Kinetic Energy is the energy an object has due to its motion
bull The KE depends on the mass and the speed
bull Ek or KE= frac12 mv2 bull E is Energy in Joules Jbull m is mass in kg v is velocity in ms
Example
bull What is the KE of a 6 kg curling stone moving at 4 ms
bull KE = frac12 mv2
bull = frac12 x 6kg x (4 ms)2
bull = frac12 x 6 x 16bull = 48 J
Activity
What is the Kinetic Energy of a 5 kg ball travelling horizontally at a speed of 10 ms
Exam QuestionA go lf ball is d ropped o u t o f a w indow w hich is 10 m above the grou nd T he ball has a m ass o f 50 g D isregard the effec ts o f a ir resis tan ce
10 m
W hat is the k inetic en ergy o f the b all just before it h its the ground
A )
10 J
B )
7 5 J
C )
5 0 J
D )
2 5 J
Potential Energybull If we lift up an object against gravity it now
has the ability to move it has the potential to fall down and use up the energy we put into it
bull Ep PE = mgh unit is Joules Jbull m is the mass in kgbull g is the acceleration due to gravity 981ms2
bull h is the height above the Earthrsquos surface m
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Kinetic Energy
bull Kinetic Energy is the energy an object has due to its motion
bull The KE depends on the mass and the speed
bull Ek or KE= frac12 mv2 bull E is Energy in Joules Jbull m is mass in kg v is velocity in ms
Example
bull What is the KE of a 6 kg curling stone moving at 4 ms
bull KE = frac12 mv2
bull = frac12 x 6kg x (4 ms)2
bull = frac12 x 6 x 16bull = 48 J
Activity
What is the Kinetic Energy of a 5 kg ball travelling horizontally at a speed of 10 ms
Exam QuestionA go lf ball is d ropped o u t o f a w indow w hich is 10 m above the grou nd T he ball has a m ass o f 50 g D isregard the effec ts o f a ir resis tan ce
10 m
W hat is the k inetic en ergy o f the b all just before it h its the ground
A )
10 J
B )
7 5 J
C )
5 0 J
D )
2 5 J
Potential Energybull If we lift up an object against gravity it now
has the ability to move it has the potential to fall down and use up the energy we put into it
bull Ep PE = mgh unit is Joules Jbull m is the mass in kgbull g is the acceleration due to gravity 981ms2
bull h is the height above the Earthrsquos surface m
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Example
bull What is the KE of a 6 kg curling stone moving at 4 ms
bull KE = frac12 mv2
bull = frac12 x 6kg x (4 ms)2
bull = frac12 x 6 x 16bull = 48 J
Activity
What is the Kinetic Energy of a 5 kg ball travelling horizontally at a speed of 10 ms
Exam QuestionA go lf ball is d ropped o u t o f a w indow w hich is 10 m above the grou nd T he ball has a m ass o f 50 g D isregard the effec ts o f a ir resis tan ce
10 m
W hat is the k inetic en ergy o f the b all just before it h its the ground
A )
10 J
B )
7 5 J
C )
5 0 J
D )
2 5 J
Potential Energybull If we lift up an object against gravity it now
has the ability to move it has the potential to fall down and use up the energy we put into it
bull Ep PE = mgh unit is Joules Jbull m is the mass in kgbull g is the acceleration due to gravity 981ms2
bull h is the height above the Earthrsquos surface m
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Activity
What is the Kinetic Energy of a 5 kg ball travelling horizontally at a speed of 10 ms
Exam QuestionA go lf ball is d ropped o u t o f a w indow w hich is 10 m above the grou nd T he ball has a m ass o f 50 g D isregard the effec ts o f a ir resis tan ce
10 m
W hat is the k inetic en ergy o f the b all just before it h its the ground
A )
10 J
B )
7 5 J
C )
5 0 J
D )
2 5 J
Potential Energybull If we lift up an object against gravity it now
has the ability to move it has the potential to fall down and use up the energy we put into it
bull Ep PE = mgh unit is Joules Jbull m is the mass in kgbull g is the acceleration due to gravity 981ms2
bull h is the height above the Earthrsquos surface m
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Exam QuestionA go lf ball is d ropped o u t o f a w indow w hich is 10 m above the grou nd T he ball has a m ass o f 50 g D isregard the effec ts o f a ir resis tan ce
10 m
W hat is the k inetic en ergy o f the b all just before it h its the ground
A )
10 J
B )
7 5 J
C )
5 0 J
D )
2 5 J
Potential Energybull If we lift up an object against gravity it now
has the ability to move it has the potential to fall down and use up the energy we put into it
bull Ep PE = mgh unit is Joules Jbull m is the mass in kgbull g is the acceleration due to gravity 981ms2
bull h is the height above the Earthrsquos surface m
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Potential Energybull If we lift up an object against gravity it now
has the ability to move it has the potential to fall down and use up the energy we put into it
bull Ep PE = mgh unit is Joules Jbull m is the mass in kgbull g is the acceleration due to gravity 981ms2
bull h is the height above the Earthrsquos surface m
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Activity
bull What is the PE of a 10 kg weight 8 m above the ground
bull PE = mgh bull = 10 kg x 981ms2 x 8mbull = 7848 J
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
ActivityA weather balloon with a mass of 40 kg including the weather instruments rises vertically in the air It passes an altitude of 200 metres at a velocity of 20 ms
20 ms
200 m
At this point what is its potential energy with respect to the ground A)
80 103 J
B)
80 102 J
C)
80 101 J
D)
80 J
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Total Mechanical Energy
bull The energy of a system transfers between Potential Energy and Kinetic Energy
bull Total Energy = PE + KEbull The PE of an object getstransferred to KE as itspeeds up bull As the PE decreases theKE increases
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Exam QuestionA small airplane with a mass of 1000 kg is flying at 60 ms at an altitude of 250 m
250 m
60 ms
What is the total mechanical energy of this airplane with respect to the ground
A)
18 106 J
B)
25 106 J
C)
43 106 J
D)
61 106 J
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Exam QuestionA s to n e w i th a m a s s o f 1 0 0 g i s t h r o w n h o r iz o n ta l l y f r o m th e to p o f a c l i f f o v e r lo o k in g th e o c e a n w i th a v e lo c i t y o f 2 0 m s D is r e g a rd th e e f f e c t s o f a i r r e s i s t a n c e
1 5 m
2 0 m s
W h a t i s th e k in e t ic e n e r g y o f th e s to n e ju s t b e f o r e i t h i t s t h e w a te r
A )
1 5 J
B )
2 0 J
C )
3 0 J
D )
3 5 J
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Total Mechanical Energybull What is the speed of a 500g rock that
drops from a height of 784 m just before it hits the ground
bull ET = KE + PE at first v = 0 msbull = frac12 mv2 + mgh since v = 0 KE = 0bull = 05kgx981ms2x784m ET = PE onlybull = 3846 Jbull As the rock approaches the ground all its
PE is transferred to KE so PE = 0 Sohellip
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Total Energy Part Deux
bull ET = PE + KEbull 3846 J = KEbull 3846 = frac12 mv2
bull 3846 = 12x 05kg x v2
bull 15384 J = v2
bull v = 392 msbull So just before it hits the ground the rock
has a speed of 392 ms
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Exam Question
A 100 g ball is thrown vertically upward from the ground with a velocity of 20 ms Disregard the effects of air resistance What is the kinetic energy of this ball after it has risen 50 metres
A) 20 J
B)
15 J
C)
10 J
D)
50 J
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Measuring Workbull Work is defined as the energy that comes
from applying a force in the same direction over a certain distance
bull W = F Δd = mad (horizontal)bull = magd (against gravity)bull = mgh (hello PE)bull Work is in Joules Jbull Force is in Newtons Nbull Distance is in metres m
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Activity
bull Eg How much work is done by a boy pushing a car with a force of 800 N over a distance of 200m
bull W = F dbull = 800 N x 200 mbull = 160 000 J = 160 kJbull
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Exam QuestionA 200 g brick falls from a wall 40 metres above the ground It hits the ground with a velocity of 85 ms
40 m
How much work did gravity do on the brick
A)
80 J
B)
72 J
C)
34 J
D)
17 J
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Effective Force
bull The Effective Force is the force component that alters the motion of an object
bull It is the component that is parallel to the movement of the object
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Components
bull The horizontal component of a vector A that is at an angle of θ from the horizontal is A cosθ
bull The vertical component of a vector A that is at an angle of θ from the horizontal
is A sinθ
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Activity
bull If a boy pulls a cart at an angle of 30 to the horizontal with a force of 100 N over a distance of 75 m how much work has he done
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Exam QuestionA sled has a mass of 10 kg A child pulls the sled a distance of 20 metres with a force of 100 N at an angle of 35deg with respect to the horizontal During this motion a force of friction of 40 N acts in the opposite direction of the motion
35
100 N
How much work is done on the sled by the child over the distance of 20 metres
A)
16 102 J
B)
11 102 J
C)
84 101 J
D)
35 101 J
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Efficiency
bull Efficiency = Work output x 100 bull Work input bull The maximum efficiency is 100bull It is a measure of what energy is lost to
friction vibration and other factors
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Questionbull An engine burns 250 000 J and loses 170 000 J to
heat and friction Calculate the enginersquos efficiencybull Useful work = 250 000 J ndash 170 000 Jbull = 70 000 Jbull Efficiency = Work output x 100 bull Work input bull = 70 000 x 100bull 250 000bull = 32
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Activity
bull Page 100 Q 10-14bull Page 101 Q 25-29bull Page 102 A-Dbull Testbull Review FOR FINAL EXAMbull Review Sheet HW for next class
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Summary
bull The Law of Conservation of Energy states that in any transfer or transformation of energy the total amount of energy remains the same
bull The form of the energy may be changed eg noise heat vibration friction
bull In situations where friction and air resistance are small enough to be ignored and where no other energy is added to the system the total mechanical energy is conserved
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Summary
bull Energy is the ability to do workbull Work is the transfer of energy (W=ΔE)bull Friction often does negative work on an
object because it removes energy from itbull Gravitational Potential Energy is the
energy of an object due to its height above the Earthrsquos surface PE = mgh
bull Kinetic Energy is the energy of a moving object KE = frac12 mv2
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
Summary
bull E total = KE + PE (before) = KE + PE (after)bull Heat is the measure of the amount of thermal
energy that flows from one body to another because of a difference in temperature
bull Work done on an object can cause an increase in the temperature of an object
bull Effective work = Fd if the object moves in the direction of the force
