Impulse – Momentum – Conservation of Momentum
Review Sheet
Momentum
 How do you calculate momentum?
Multiply mass x velocity.
 What two factors affect the momentum of an object?
Mass and velocity.
 As the speed of an object increases what happens to the momentum?
The momentum increases.
 If you double the speed of an object what happens to momentum?
If you double the speed you double the momentum. Similarly, if you were to double the
mass, the momentum of a moving object would double as well.
 What are the units of momentum?
Kg m/s
 Which of the following has the largest momentum: a 50-kg student running at 3 m/s, a
300-kg car that is at rest, or a 2 kg dog that is running at 1 m/s?
A 50 kg student running at 3 m/s has a momentum of 150 kg m/s.
The car since it is at rest has a momentum of 0.
The dog has a momentum of 2 kg m/s.
Impulse
 Impulse is equal to the change in an object’s momentum.
 What are the units for impulse?
Newton seconds.
 Are the units for impulse equivalent to the units for momentum?
Yes. A newton is equivalent to a kg m/s2, thus the units of impulse breakdown to kg m/s.
Impulse – Momentum
 Airbags reduce injury by increasing what variable?
Time.
 Explain the strategy in catching a water balloon during the balloon toss experiment.
Students would cradle the water balloon to increase the contact time which decreases the
force of impact.
 What can a baseball player do to increase the momentum of his swing? (swing as fast as
possible, follow through, and increase contact time)
 The impulse necessary to change an object’s momentum by 5 kg m/s is 15 kg m/s
because impulse is equal to momentum.
Collisions
 List one example of an elastic collision.
Two billiard balls bouncing off each other. Any example would suffice that entails two
objects colliding and bouncing.

Elastic collisions involve two objects bouncing off each other while an inelastic collision
involves two objects sticking together.
 When two objects hit each other an elastic collision occurs.
 What is the law of conservation of momentum? The momentum before a collision is
equal to the momentum after a collision.
 Explain the physics behind air bags, seat belts and padded dashboards.
The stopping time of a car in a collision is very short even when crumpling occurs. A
passenger without a seat belt will have a momentum that drops from very large value to
zero when hitting the windshield, the steering wheel, or dashboard. Seat belts are made of
a very strong fabric that stretches slightly when a force is applied. Stretching extends
the time over which the passenger comes to a stop and results in less force being exerted
on the person’s body.
Air bags work together with seat belts to make cars safer. An air bag inflates when the
force applied to the front of a car reaches a dangerous level. The air bag deflates slowly
as the person’s body applies a force to the bag upon impact. The force of impact from the
body pushes the air out of small holes in the air bag, bringing the person to a gradual
stop.
Padded dashboards increase the contact time thus decreasing the force.
Word Problems
 Calculate the impulse necessary to change the momentum of a 100 kg object by 20 kg
m/s.
Looking For
Given
Relationship
Solution
Impulse
m=100 kg
Ft=mv
20 N s
p=20 kg m/s

Calculate the momentum of a 400-kg car traveling at 10 m/s.
Looking For
Given
Relationship
momentum
m=100 kg
p=mv
v=10 m/s
Solution
1000 kg m/s

Jack throws a 2-kg baseball with a velocity of 3 m/s. Calculate the impulse necessary to
stop this ball.
Looking For
Given
Relationship
Solution
Impulse
m=100 kg
Ft=mv
6Ns
v=3 m/s

What force is needed to stop a 500-kg car moving at 5 m/s in 2 seconds?
Looking For
Given
Relationship
Solution
force
m=500 kg
Ft=mv
1250 N
v=5 m/s
t= 2 seconds