Name __________________________
Date_____________
Momentum - Final Review
THE BIG IDEA:
The big idea behind momentum is that is CONSERVED for all collisions as long as external forces don’t
interfere. An interfering force would be something like a “brick wall”.
You also need to remember units for each component of the equation:
Units used in momentum
Mass: kilograms
Velocity: meters/sec
Time: seconds
Distance: kilometers.
The equations are :
First idea:
Second idea:
Momentum = mass * speed (p = mv)
An impulse changes momentum. The amount of change depends on the amount of
Force that acts on an object and the length of time it acts
An impulse is a force * time interval
(J = Ft)
The relationship between an impulse and the change in momentum is (Ft = mv)
(this usually means the velocity changes)
Third idea:
Bouncing requires a greater impulse than not bouncing
When you bounce (or when anything bounces) there is an impulse required to bring an
object to a stop AND make it go back up into the air. So when something bounces it has
an impulse that is bigger than when something doesn’t bounce.
Fourth idea
Momentum is conserved (M1v1 + m2v2 = m1v1 + m2v2
(this means the momentum in the “before system” = the momentum in
the “after system”
Net p before collision = Net p after collisions
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Name __________________________
Date_____________
Fifth idea: Collisions cause some exchange of momentum, but the total momentum is the same)
An elastic collision is one where two objects interact and momentum is conserved, but perfectly
exchanged.
a. The objects DON’T permanently deform (get dented)
b. There is no heat generated Examples: marbles hitting each other, protons colliding
An inelastic collisions are collisions where momentum is conserved ..BUT not “perfectly exchanged”
a. The objects are permanently deformed
b. Heat is generated
c. If they are totally inelastic collisions, the two objects will “stick together”
Examples: cars colliding, a skater “jumping” into the arms of another skater (they “stick together”.
The final idea, which is actually the first statement on the page, is that momentum is conserved. That
means if you are looking at a system that has only INTERNAL forces and momentum, the momentum a
system starts with is the same momentum that it ends with.
So if your system consists of two marbles that are moving toward each other, the total momentum of
the system is the momentum of the first marble + the momentum of the second. When they hit each
other, they will change speed or direction, or both, but the total momentum of the two marbles will
not change! MOMENTUM IS CONSERVED!
So..based on what I have told you, answer the following questions
1. A moving car has momentum because:
a. It has velocity
b. It has mass
c. Both a and b
2. If two cars with the same mass(Cars A and B) are moving, but one (Car B) is moving at twice
the speed of Car A
a. Both cars have the same momentum
b. The momentum of car B is twice the momentum of car A
c. The momentum of car B is more than car A, but it can’t be calculated with the
information given.
3. Two cars move down a hill at a constant velocity. Car C is much larger than Car D. The car
that has greater momentum is:
a. Car C because it is moving faster
b. Car D because it has less mass
c. Car C because it has more mass.
4. A cannon shoots a cannon ball. The momentum of the cannon as compared to the cannon ball
is:
a. The same as the cannon ball
b. Greater than the cannon ball
c. Less than the cannon ball
5. A car is
a.
b.
c.
d.
idling in the parking lot its momentum is
Greater than a car with the engine turned off
Less than a car that is moving
Zero
Both b and c
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Name __________________________
Date_____________
e. All of the above
6. What is the momentum of a 2 kg toy car travelling at 3 meters/second
a. .67 kgm/s
b. 6 kgm/s
c. 1.5 kg m/s
d. It cannot be calculated
7. Which has a greater momentum: a 15 kg object moving at 4 m/s (object A) or a 25 kg object
moving a 2 m/s (Object B)
a. Object A
b. Object B
c. Both are moving at the same rate
8. A change in momentum depends on the __________________ that acts on an object and the
__________________ it acts
a. Mass, amount of time
b. Distance, amount of time
c. Force, amount of time
9. The larger the impulse:
a. The smaller the change in momentum
b. The larger the change in momentum
c. The more stubborn the momentum will be, it is like a Jr. that doesn’t like math.
10. The relationship between impulse and the change in momentum is
a. Ft = mv
b. Fd = mv
c. The greater the force of an impulse, or the distance over which an impulse is applied
or both, the greater the change in momentum
d. Both b and c.
11. Which would produce a greater change the momentum of an object
a. A large force in a small amount of time
b. A small force over a large amount of time
c. You cannot tell from the information given
12. An object has a momentum of 12 kgm/s. A force of 10 N is applied to the object. What is the
amount of time this force must be applied.
a. 1 second
b. 12 seconds
c. 1.2 seconds
d. 0.8 seconds
13. To obtain the highest change in the momentum of an object you should
a. Apply a large force for a short time
b. A large force for a long time
c. A small force for a long time
14. When an egg hits the floor, it will probably break. Yet if you drop an egg of the same mass
onto a sheet being held by students, it will not break. Why?
a. There is less force on the egg
b. The force to the egg occurs over time, so the average force is less
c. The egg accelerates less.
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Name __________________________
Date_____________
15. Suppose that you were involved in a head-on collision and your airbag did not deploy. Instead,
your face hit a padded dashboard. How might the “force” on your face be different, than if
the airbag had actually been deployed. Be sure to explain why this would happen.
The increase in the time for the change in momentum results in a decrease in the force that acts on
the body.
16. When you are boxing, you can lessen the blow from your opponent by:
a. Moving “into the punch”
b. Moving “away” as you are being punched
17. Two steel balls collide. The first (A) has a momentum of 1.5 kgm/s and the second (B) has a
momentum of 1 kgm/s. In an elastic collision the momentum of marble A as compared to
marble B will be:
a. The same as before the collision, but moving in the opposite direction
b. Will be equal. When the two balls collide each will end up with ½ the total momentum
c. Reversed. The two steel balls will exchange momenta.
X
18. Sam and Harry are each standing on a skateboard on a “frictionless” surface. Sam has a mass
of 90 kg and Harry’s mass is 110 kg. Which of the skateboarders has
a. More mass - Harry
b. More velocity - ?
c. More momentum - ?
X
19. What is different about the momentum of each skateboarder?
20. You are learning how to ski, and the bozo hotshot skier who is trying to show off collides with
you. You both “stick” together and move with a common velocity. What can you say about the
combined momentum? (choose all that are correct)
a.
b.
c.
d.
Momentum is conserved
Momentum is not exchanged perfectly
The collision is inelastic
The collision is elastic
21. When a dish falls onto the floor is the impulse different than when it falls onto a thick carpet?
a. Yes, because fxt is greater when it hits the floor
b. No, because f x t is the same.
22. What factors affect how much an object’s momentum will change
a. Force
b. Time
c. Both force and time
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Name __________________________
Date_____________
23. A karate expert strikes the blocks in such a way that her hand is made to “bounce back”. This
means that the impulse applied to the boards she is trying to break is
a. Increased
b. Decreased
24. How does the impulse of an object that bounces compare to the impulse of that same object
when it simply “stops”?
a. It is the same
b. It is greater when it bounces
c. It is less when it bounces
25. The Law of Conservation of Momentum says:
a. Momentum never changes
b. Change in momentum only occurs if a force outside the system acts on a system
c. Change in momentum occurs when any force (external or internal) acts on a system
26. In which scenario would NO change in the momentum of the object be possible?
a. You pushing on the dashboard from inside the car
b. You pushing on the back of the car
c. You dribbling a basketball
d. The molecules inside the basketball moving
e. Both a and d
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