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Name: __________________________________
Science 20 – Unit B – Changes in Motion
Science 20
Unit B – Changes in Motion
General Outcome 2: Students will describe and analyze the law of conservation of
momentum for one-dimensional collisions and change in momentum (impulse) to
explain how force affects motion.
Specific Outcome 2.1sts: Explain the goal of technology is to provide solutions to
practical problems
Specific Outcome 2.6: Apply Newton’s third law of motion to explain the
interaction between two objects
Specific Outcome 2.2: Apply the law of conservation of momentum to one-
dimensional collisions and explosions
Specific Outcome 2.7: Relate, quantitatively, potential and kinetic energy to
work done
Textbook pages 257 – 281
Automobile technology has evolved to solve practical problems.
Automobile Technology
of the Past
Automobile Technology
of the Present
How the Change in Technology
Helped Reduce Injury metal front and rear
bumpers welded solidly to
the main frame of the
automobiles
large plastic bumpers
attached through shock
absorbers to a collapsible
frame
increased the time of the impact
between the vehicle and the
obstacle, reducing the force
required to stop the vehicle
solid metal frame collapsible frame with
crumple zones
increased the time of the impact
between the vehicle and the
obstacle, reducing the force
required to stop the vehicle
metal dashboard, hard
plastic steering wheel
solidly attached to steering
mechanisms of the
automobile
padded dashboard and
interior with a collapsible,
shock-absorbing steering
wheel
increased the time of the impact
between the occupants and the
interior of the vehicle, reducing the
force required to stop the
occupants
no seat belts or air bags seat belts and driver- and
passenger-side air bags;
often side-impact air bags
increased the time of the impact
between the occupants and the
interior of the vehicle, reducing the
force required to stop the
occupants
seat belts: spread the force
needed to decelerate occupants
over the larger, stronger parts of
the body—the pelvis, chest, and
shoulders
seat belts: keep occupants in their
vehicles during a crash
Name: __________________________________
Science 20 – Unit B – Changes in Motion
Sum of momentum before = sum of momentum after
TYPES OF COLLISIONS
There are three types of collisions that are involved when a vehicle is involved in a
collision.
PRIMARY COLLISION: occurs when a vehicle collides with another object, such as a
vehicle
SECONDARY COLLISION: occurs when the occupant collides with the interior of the
vehicle
TERTIARY COLLISION: occurs when the occupant’s internal organs collide within the
occupant’s body.
NEWTON’S THIRD LAW OF MOTION
Newton’s third law of motion states that whenever one object exerts a force on a
second object, the second object exerts an equal but opposite force on the first
object.
�⃗⃗� 𝟏 𝒐𝒏 𝟐 = �⃗⃗� 𝟐 𝒐𝒏 𝟏
CONSERVATION OF MOMENTUM
The Law of Conservation of Momentum states that if the net force acting on a system is
zero, the sum of the momentum before an interaction equals the sum of the
momentum after the interaction.
∑𝑝 𝑏𝑒𝑓𝑜𝑟𝑒 = ∑𝑝 𝑎𝑓𝑡𝑒𝑟
patriots-in-motion.wikispaces.com
Name: __________________________________
Science 20 – Unit B – Changes in Motion
There are 3 different types of collisions that follow the law of conservation of
momentum.
physics.tutorvista.com
𝑚1𝑣 1 + 𝑚2𝑣 2 = (𝑚1 + 𝑚2)𝑣 1 𝑎𝑛𝑑 2
Hit and stick
www.physicsclassroom.com
Hit and rebound
𝑚1𝑣 1 + 𝑚2𝑣 2 = 𝑚1𝑣 ′1 + 𝑚2𝑣 ′2
www.kwantlen.ca
Explosion
(𝑚1 + 𝑚2)𝑣 1 𝑎𝑛𝑑 2 = 𝑚1𝑣 ′1 + 𝑚2𝑣 ′2
Name: __________________________________
Science 20 – Unit B – Changes in Motion
Example 10
A 10 000 kg freight car travelling west with a velocity of 1.5 m/s collides with a 20 000 kg
freight car at rest. After the collision, the freight cars stick together. Determine the
velocity of the freight cars after the collision.
Because the objects are locked
together, they can be treated as
one object.
Name: __________________________________
Science 20 – Unit B – Changes in Motion
Example Problem 11
A 3.0 kg ball rolling east with a velocity of 1.5 m/s collides with another 6.0 kg ball at rest.
After the collision, the first ball rebounds and is travelling at a velocity of 0.50 m/s[W].
a. Determine the velocity of the second ball after the collision.
b. Determine the momentum values of the balls before and after the collision.
a.
b.
Name: __________________________________
Science 20 – Unit B – Changes in Motion
Example Problem 12
A 0.020 kg firecracker at rest explodes into two pieces. If a 0.015 kg piece flies off to the
right at a velocity of 3.00 m/s, determine the velocity of the other 0.0050 kg piece.
Name: __________________________________
Science 20 – Unit B – Changes in Motion
mass g = 9.81 m/s2
height above reference point
DESIGNING HELMETS
Momentum, force, collisions, and energy are all considered when designing helmuts.
WORK is the transfer of energy from one object or system to another when a force is
applied over a distance.
𝑾𝒐𝒓𝒌 = 𝑭𝒐𝒓𝒄𝒆 × 𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆
𝑾 = �⃗⃗� × 𝒅
Work is measured in joules (J).
ENERGY is the ability to do work. Energy is measured in joules(J). since both work and
energy are measured in joules, work can be related to energy.
LAW OF CONSERVATION OF ENERGY states that when energy is changed from one form
to another, the total energy of the system remains the same.
GRAVITATIONAL POTENTIAL ENERGY is energy due to the position of an object above
Earth’s surface.
𝑬𝒑(𝒈𝒓𝒂𝒗) = 𝑾
𝑬𝒑(𝒈𝒓𝒂𝒗) = 𝑭 × ∆𝒅
𝑬𝒑(𝒈𝒓𝒂𝒗) = 𝒎𝒈𝒉
KINETIC ENERGY is energy due to the motion of an object.
𝐸𝑘 =1
2𝑚𝑣2
Name: __________________________________
Science 20 – Unit B – Changes in Motion
Example Problem 13
An egg test dummy is fitted with a helmet and sealed in a plastic bag. The mass of the
egg, helmet, baggie, and paper clamp is 0.085 kg. The egg and its accessories are
attached to the swing and pulled back so that they are now 0.40 m above the
reference level. The egg is released and swings down to collide with a cement block.
a. Calculate the gravitational potential energy of the egg and its accessories.
b. Determine the kinetic energy of the egg and its accessories when it collides with
the cement block. Explain how this energy is transformed in the collision.
c. Calculate the speed of the egg and its accessories the moment before impact.
d. Calculate the magnitude and direction of the momentum of the egg and its
accessories just before impact.
e. Assume the egg and its accessories stop immediately after impact. Use this
information to approximate the change in momentum of the bag and its
contents.
f. Calculate the impulse required to stop the bag during impact.
g. If the impact lasts for 0.040 s, determine the force that acted upon the bag and
its contents during the collision using the equation for impulse.
h. Determine the acceleration of the egg and its accessories over the 0,040 s.
i. Use Newton’s second law to confirm your answer to question g, by calculating
the force that acted on the bag and its contents.
Name: __________________________________
Science 20 – Unit B – Changes in Motion
Practice questions:
Page 270 #17-19