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 rollerskating, 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 2kg 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 4.0kg 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 5.0kg chunk of putty moving at 10.0 m/s collides with and sticks to a 7.0kg
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


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 10kg 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 8kg blob of clay moving horizontally at 2 m/s hits a 3kg blob of clay at
rest. What is the speed of the two blobs stuck together immediately after the collision?


29.

A 40kg football player leaps through the air to collide with and tackle a 50kg
player heading toward him, also in the air. If the 40kg player is heading to the right at 9 m/s and
the 50kg 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 50kg cart moving at 100 km/h collides headon with an approaching 50kg cart
moving at 10 km/h (in the opposite direction). If the two carts stick together, what will be their
speed?


31.

A 30kg girl and a 50kg boy face each other on frictionfree 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 70kg freefloating astronaut fires 0.10kg of gas at a speed of 30 m/s from
her propulsion pistol. What is the astronaut's recoil speed?
