Momentum, Work, and Power Test B - L
(1) The momentum of an object is defined as the object’s ___.
(a) force times its acceleration
(d) mass times its acceleration
(b) force times the time interval
(e) mass times its velocity
(c) velocity times the time interval
(2) If the momentum of an object changes and its mass remains constant ___.
(a) there is a force acting on it
(d) its velocity is changing
(b) all of the above
(e) none of the above
(c) it is accelerating
-----------------------------------------------------------------------------------------------------------Carts A and B are an isolated system on
a frictionless air track. Cart A (moving
to the right) hits cart B (at rest) as
shown in the drawing. They stick together
and both move to the right after the collision.
(3) BEFORE the collision, the nonzero part of
the momentum of the system (A and B) is ...
(a) shared by A and B
(d) none of these.
(b) zero
(e) all in cart A
(c) all in cart B
At rest
B
A
BEFORE COLLISION
A
B
AFTER COLLISION
(4) The velocity of cart A after the collision will be ___ its velocity before the collision.
(a) equal to
(b) faster than
(c) slower than
-----------------------------------------------------------------------------------------------------------(5) A 0.2 kg golf ball is traveling at 50 m/sec. After air resistance acts on it for 1.0 seconds, it has slowed down to 30
m/sec. The CHANGE IN MOMENTUM for this golf ball equals ___ kg•m/sec.
(a) 6
(b) 4
(c) 10
(d) -4
(e) none of these
(6) For the golf ball in #5 above, the IMPULSE given to the ball by the force of the air equals ___.
(same choices as #5 above) Same as above
-----------------------------------------------------------------------------------------------------------(7) When a karate expert executes a swift blow and severs a cement block with her bare hand.
(a) The force on both the block and the expert’s hand have the same magnitude.
(b) all of the above are all true statements
(c) The time of impact on both the block and the expert’s hand have the same magnitude.
(d) The impulse on both the block and the expert’s hand have the same magnitude.
(8) An isolated system consists of two objects, A and B. They have a collision where A slows down and B speeds up.
The amount of momentum lost by A is ____ the amount of momentum gained by B.
(a) equal to
(b) less than
(c) greater than
(d) cannot be determined without additional information.
(9) A 500 kg cannon is at rest on a horizontal frictionless surface. It fires a 5 kg cannonball to the right at 40 m/sec. The
recoil velocity of the cannon is ___ m/sec.
(a) -2.5
(b) -0.4
(c) -100
(d) -25
(e) none of these
(10) A cannon recoils from launching a cannonball. The speed of the cannon’s recoil is small because the ___.
(a) force against the cannon is relatively small
(b) momentum of the cannon is unchanged
(c) something was thrown in the direction opposite to that in which she wants to go
(d) cannon has far more mass than the cannonball
(e) all of the above is correct
(11) A 2 kg bat hits a 0.5 kg ball, which was at rest. After the hit the ball is moving at 10 m/sec. The bat touches the
ball for 0.02 seconds. The FORCE exerted on the ball by the bat equals ____ N.
(a) 500
(b) 1000
(c) 125
(d) 250
(e) none of these
(12) A rubber ball and a lump of putty have equal masses. They are thrown with equal speed against a wall. The ball
bounces back with nearly the same speed with which it hit. The putty sticks to the wall. Which object experiences
the greater change in momentum?
(a) the ball
(c) both experience the same change of momentum
(b) the putty
(d) cannot be determined
(13) An 80 kg cart moving 70 km/hr collides head-on with an approaching 120 kg cart moving 40 km/hr (in the opposite
direction). If the two carts stick together, what will be their speed in km/hr?
(a) 6
(b) 8
(c) 4
(d) 0
----------------------------------------------------------------------------------------------------------(14) If you want to build a container to protect an egg when it is dropped, the surface which touches the egg should be
___ in order to ___ the time of collision.
(a) soft, decrease
(b) hard, increase
(c) hard, decrease
(d) soft, increase
(15) kg•m/sec is a unit of ___, and kg•m/sec2 is a unit of ___.
(a) force, momentum
(d) momentum, force
(b) impulse, momentum
(e) none of these
(c) momentum, impulse
Driver #1 and driver #2 have the same mass and are in separate cars traveling at 65 mi/hr (legally on the interstate).
Both cars hit a parked truck and come to rest. Driver #1 is stopped when she hits the steering wheel. Driver #2 is
stopped by an inflated air bag mounted on the steering wheel.
CHOICES FOR QUESTIONS BELOW:
(a) equal to
(b) greater than
(c) less than
(16) The change in momentum for driver #1 is __a_ the change in momentum for driver #2.
(17) The impulse on driver #1 is _a__ the impulse on driver #2.
(18) The time of collision for #1 is _c__ the time of collision for #2.
(19) The force (and damage) for driver #1 is _b__ the force (and damage) for driver #2.
----------------------------------------------------------------------------------------------------------(20) When you jump off a step, you usually bend you knees as you reach the ground. By doing this, the time of impact is
about 10 times more than what it would be in a stiff-legged landing and the average force on your body is ___.
(a) reduced by 10 times
(c) increased by 100 times
(b) increased by 10 times
(e) it does not change
(d) decreased by 100
(21) A rock hits a wall. Compared to the force that the rock exerts on the wall, the force on the ball exerted by the wall
is ___.
(a) smaller
(b) larger
(c) the same
(22) Refer to #21. The impulse on the wall by the ball is _____ the impulse on the ball by the wall.
(a) the same as
(b) larger than
(c) smaller than
(23) Refer to #21. The change of momentum of the wall _____ the change of momentum on the ball by the wall.
(a) the same as
(b) larger than
(c) smaller than
(24) Momentum is conserved for ___.
(a) elastic collisions only
(c) both elastic and inelastic collisions
(25) Momentum is a vector quantity
(a) True
(b) False
(b) inelastic collisions only