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Do Now:
Determine the change in potential energy if a 3 kg box is raised from a height of 1 m to a height of 3 m.
A force of 56 N is applied to a box at an angle of 41˚. If the box moves a distance of 0.23 m, what is the work done on the box?
Do Now (2/1/12):
Conservation of Energy:
Energy cannot be created or destroyed. The total amount of energy in a system is conserved over time.
Rollercoaster
http://www.physicsclassroom.com/mmedia/energy/ce.cfm
Example:
1. What is the total energy at each given point?2. Which type of energy gets larger as the skier falls?3. Which type of energy gets smaller as the skier
falls?
Do Now (2/2/12):
A 100 kg car on a rollercoaster begins 60 m above the ground.
1. What is the car’s potential energy at the top?
2. What is the car’s total energy at the top?3. What is the car’s total energy at the bottom?4. What type of energy is equivalent to the
total energy at the bottom?
*if you weren’t here yesterday, please just write the questions!
Review: Conservation of Energy:
Energy cannot be created or destroyed. The total amount of energy in a system is conserved over time.
Strategies for solving Energy problems
Calculate the total energy E as soon as possible
The PE at the reference level is 0 – therefore at the reference level:
At the top PE is a maximum – therefore KE is 0 and
KEEtotal
PEEtotal
Do Now:
You lift a 2 kg textbook from the floor to shelf 2.1 m above the floor.
1. What is the book’s gravitational potential energy relative to the floor?
2. What is its gravitational energy relative to your head, assuming you’re 1.65 m tall?
Do Now (2/3/12):
In this unit, we learned the food is a form of stored energy. How many M&M candies do you think you would need to replace the energy you’d burn if you climbed the steps from the ground floor to the third floor?
LAB!
Read over the lab and fill out #’s 1 and 5 on the Results/Calculations sheet
ONE person from each group will get the hall pass at a time.
1. Count the stairs2. Measure the height per stair3. One person at a time climbs the stairs
and times themselves 4. Everyone else in the classroom should
be working on calculations
LAB! Factor label conversion
To find the energy in EACH candy
Jcal
J
tbsp
cal
MM
tbspMMEcandy ____
1
4190
1
55
&15
1&1
candy
g
E
UCandies
#
Strategies for solving Energy problems
Calculate the total energy E as soon as possible
The PE at the reference level is 0 – therefore at the reference level:
At the top PE is a maximum – therefore KE is 0 and
KEEtotal
PEEtotal
Practice:
Take 15 min to work on Practice Problems #5-7 on p. 254 in your classroom textbook. We will go over them at the end of class.
Example: Conservation of EnergyA 10 kg ball is dropped from a cliff 50 m
tall.1. What is the ball’s potential energy
before being dropped?2. What is the ball’s total energy before
being dropped?
Example: Conservation of EnergyA 10 kg ball is dropped from a cliff 50 m
tall.3. At a height of 30 m, what is the kinetic
energy of the ball?
Example: Conservation of EnergyA 10 kg ball is dropped from a cliff 50 m
tall.4. When it reaches of velocity of 20 m/s,
what is the potential energy?
Do Now (2/6/12):
A 10 kg ball is dropped from a 50 m cliff.
1. What is the potential energy at the top?
2. What is the work done?3. What is the kinetic energy at
the bottom?4. What is the velocity of the
stone right before it hits the ground?
Reminders:
TUESDAY 2/7/12 is the LAST DAY to MAKE UP QUIZZES. Quizzes not made up by then will be filled in with a score of zero.
Keep your homework for another night; use your Conservation of Energy sheet to make a NOTECARD for tomorrow’s quiz.
Energy and Power LABS are due tomorrow
Popper Lab
Use TWO HANDS to carry the balances
Raise your hand if you have any QUESTIONS
DO NOT LOSE YOUR POPPER!!!!!!!!!!!! This will result in a grade deduction.
Do Now (2/7/12):
1. In our popper lab yesterday, what form of energy does the popper have before it pops?
2. What was the popper’s initial source of energy?
3. Was mechanical energy conserved throughout the motion of the popper?
4. What happened to the energy after the popper stopped moving?