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 Momentum HW Study Guide2

Momentum Homework 2

Multiple Choice
Identify the choice that best completes the statement or answers the question.
 

 1. 

Momentum of a system is conserved only when
a.
there are no internal forces acting on the system.
b.
the system is not moving.
c.
there are no forces acting on the system.
d.
there is no net external force acting on the system.
e.
the system has zero momentum.
 

 2. 

A collision is considered elastic if
a.
there is no lasting deformation.
b.
the objects don’t stick together.
c.
the objects that collide don't get warmer.
d.
after the collision, the objects have the same shape as before the collision.
e.
all of the above
 

 3. 

Suppose a girl is standing on a pond where there is no friction between her feet and the ice. In order to get off the ice, she can
a.
bend over touching the ice in front of her and then bring her feet to her hands.
b.
walk very slowly on tiptoe.
c.
get on her hands and knees and crawl off the ice.
d.
throw something in the direction opposite to the way she wants to go.
e.
all of the above will work
 

 4. 

Suppose a cannon is made of a strong but very light material. Suppose also that the cannonball is more massive than the cannon itself. For such a system
a.
conservation of momentum would not hold.
b.
conservation of energy would not hold.
c.
the cannon would travel faster than cannonball.
d.
the force on the cannonball would be greater than the force on the cannon.
e.
recoil problems would be lessened.
 

 5. 

Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a higher
a.
acceleration.
b.
momentum.
c.
speed.
d.
all of the above
e.
none of the above
 

 6. 

A cannon fires a cannonball. The speed of the cannonball will be the same as the speed of the recoiling cannon
a.
if the mass of the cannonball equals the mass of the cannon.
b.
because momentum is conserved.
c.
because velocity is conserved.
d.
because both velocity and momentum are conserved.
e.
none of the above
 

 7. 

A moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, the velocity of the combined cars after the collision is
a.
zero.
b.
one half as large.
c.
the same.
d.
twice as large.
e.
More information is needed to say.
 

 8. 

Two gliders having the same mass and speed move toward each other on an air track and stick together. After the collision, the velocity of the gliders is
a.
twice the original velocity.
b.
one half the original velocity.
c.
zero.
d.
the same as the original velocity.
e.
There is not enough information to say.
 

 9. 

A piece of putty moving with 2 kgm/s of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both are set in motion with a combined momentum that is
a.
less than 2 kgm/s.
b.
2 kgm/s.
c.
more than 2 kgm/s.
d.
There is not enough information to say.
 

 10. 

The force that accelerates a rocket into outer space is exerted on the rocket by
a.
the exhaust gases.
b.
Earth's gravity.
c.
atmospheric pressure.
d.
rocket's wings.
e.
none of the above
 

 11. 

Suppose an astronaut in outer space wishes to toss a ball against a very massive and perfectly elastic concrete wall and catch it as it bounces back. If the ball is as massive as the astronaut, then
a.
the astronaut's time between catches will decrease as the game progresses.
b.
the astronaut will never catch the first bounce.
c.
the astronaut will catch one bounce only.
d.
none of the above
 

 12. 

Superman is at rest in space when he throws an asteroid that has more mass than he does. Which moves faster, Superman or the asteroid?
a.
Superman
b.
The asteroid
c.
They both move at the same speed.
 

 13. 

While roller-skating, Granny collides with her tiny grandson Ambrose who is at rest. Ignoring any friction effects, Ambrose's speed after the collision will be greatest when
a.
Granny catches him and they both move together.
b.
he and Granny make a bouncing collision, each going in opposite directions.
 

 14. 

A 2-kg ball is thrown at 3 m/s. What is the ball's momentum?
a.
2 kg·m/s
b.
3 kg·m/s
c.
6 kg·m/s
d.
9 kg·m/s
e.
none of the above
 

 15. 

A 4.0-kg ball has a momentum of 20.0 kg·m/s. What is the ball's speed?
a.
0.2 m/s
b.
5.0 m/s
c.
20.0 m/s
d.
80.0 m/s
e.
none of the above
 

 16. 

A ball is moving at 6.0 m/s and has a momentum of 24.0 kg·m/s. What is the ball's mass?
a.
0.3 kg
b.
4.0 kg
c.
24.0 kg
d.
144.0 kg
e.
none of the above
 

 17. 

A 5.0-kg chunk of putty moving at 10.0 m/s collides with and sticks to a 7.0-kg bowling ball that is initially at rest. The bowling ball with its putty passenger will then be set in motion with a momentum of
a.
0 kg·m/s.
b.
2.0 kg·m/s.
c.
15.0 kg·m/s.
d.
50.0 kg·m/s.
e.
more than 50.0 kg·m/s.
 

True/False
Indicate whether the statement is true or false.
 

 18. 

Momentum is defined as an object's mass times its velocity.
 

 19. 

If the net external force acting on a system is zero, then the total momentum of the system is zero.
 

 20. 

When two objects collide and completely bounce apart with no lasting deformation or generation of heat, the collision is said to be elastic.
 

 21. 

When two objects collide and stick together, the collision is said to be inelastic.
 

 22. 

Perfectly elastic collisions between large objects are uncommon in the everyday world.
 

Essay These are not graded online.  These should be done on your practice worksheet given to you in class.  To check the answers to these click on the answers link on the CP intro page. 
 

 23. 

In terms of momentum change, explain why it is best to "give" when catching a baseball. Provide other examples of situations in which you want to lengthen the impact time in a collision.
 

 24. 

Why would a .22 rifle bullet travel farther than a .22 pistol bullet shot at the same angle?  (This question refers directly to one of your study guide questions. Use the concept of Impulse in your explanation!)
 

 25. 

What does it mean to say that momentum is conserved? Give an example where momentum is conserved in a collision.
 

 26. 

A railroad diesel engine coasting at 12 km/h runs into a stationary flatcar. The diesel weighs 5 times as much as the flatcar. Assuming the cars couple together, how fast are they moving after the collision?
 

Problem
 

 27. 

A 10-kg cement block moving horizontally at 6 m/s plows into a bank of sand and comes to a stop in 2 s. What is the average impact force on the bank?
 

 28. 

An 8-kg blob of clay moving horizontally at 2 m/s hits a 3-kg blob of clay at rest. What is the speed of the two blobs stuck together immediately after the collision?
 

 29. 

A 40-kg football player leaps through the air to collide with and tackle a 50-kg player heading toward him, also in the air. If the 40-kg player is heading to the right at 9 m/s and the 50-kg player is heading toward the left at 2 m/s, if the larger player stops his momentum as they hit and all the momentum is transferred to the smaller player, how fast will the smaller player be sent backwards?
 

 30. 

A 50-kg cart moving at 100 km/h collides head-on with an approaching 50-kg cart moving at 10 km/h (in the opposite direction). If the two carts stick together, what will be their speed?
 

 31. 

A 30-kg girl and a 50-kg boy face each other on friction-free roller skates. The girl pushes the boy, who moves away at a speed of 3 m/s. What is the girl's speed?
 

 32. 

A 70-kg free-floating astronaut fires 0.10-kg of gas at a speed of 30 m/s from her propulsion pistol. What is the astronaut's recoil speed?
 



 
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