Physics 1A Winter 2009: Quiz 4
Version A
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Closed book. No work needs to be shown for multiple-choice questions.
1. An elastic collision is one in which:
a. momentum is not conserved but kinetic energy is conserved.
b. total mass is not conserved but momentum is conserved.
-> c. kinetic energy and momentum are both conserved.
d. momentum is conserved but kinetic energy is not conserved.
e. the kinetic energy of the system increases after the collision.
2. A woman weighing 730N stands in the middle of a frozen pond of radius 5m. She is unable
to get to the other side because of a lack of friction between her shoes and the ice. To propel
herself, she throws a 1.2kg backpack horizontally towards the south shore at a speed of 5m/s.
How long does it take her to reach the north shore?
a. 30s
-> b. 60s
c. 90s
d. 120s
e. 150s
3. The law of conservation of momentum applies to two colliding objects only if:
a. there is no change in kinetic energy of the system.
b. the two colliding objects stick together.
c. the collision is inelastic.
-> d. the net external force on the system is zero.
e. the collision is elastic.
4. A bowling ball of mass 5.0 kg initially moves with a speed of 3.0 m/s in the +x direction. It
then hits the wall and bounces back with the same speed in the in the –x direction. What was
the change in momentum of the ball?
-> a. –30 kg(m/s).
b. –15 kg(m/s).
c. 0 kg(m/s).
d. +15 kg(m/s).
e. +30 kg(m/s).
5. A cart is moving at constant speed in the +x direction. At some point, a rocket is launched
from the cart. What is the change in speed of the car after the rocket launch if (a) the rocket
launcher on the cart is positioned straight up when launching the rocket? (b) the rocket
launcher is positioned at a 45 degree angle with the +x direction?
a. no change in speed either way.
b. speed decreases in both cases.
c. (a) speed increases, (b) speed decreases.
-> d. (a) speed is unchanged, (b) speed decreases.
e. none of the above.
02.27.08
Physics 1A Winter 2009: Quiz 4
Version A
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6. Blocks A and B are moving toward each other. Block A has a mass of 2.0 kg and a velocity
of 50 m/s, while block B has a mass of 4.0 kg and a velocity of –25 m/s. The blocks stick
together after the collision. The kinetic energy lost during the collision is:
a. 0.
b. 1250 J.
-> c. 3750 J.
d. 5000 J.
e. 5600 J.
7. Mitch throws a 100 g lump of clay at a 500 g target, which is at rest on a horizontal surface.
After impact, the target, including the attached clay, slides 2.1 m before stopping. If the
coefficient of kinetic friction between the target and the surface is µk = 0.50, find the speed of
the clay before impact.
a. 4.5 m/s.
b. 12 m/s.
-> c. 27 m/s.
d. 36 m/s.
e. 5.0 m/s.
8. Two identical balls are involved in a head on elastic collision. Before the collision, one of the
balls is at rest, while the other is moving towards it in the +x direction. Which of the
following statements is most accurate?
-> a. After the collision one ball is at rest, and the other is moving in the +x direction at
the initial speed of the moving ball.
b. After the collision both balls are moving in the +x direction.
c. After the collision one ball is moving in +x while the other is moving in –x direction
at different speeds.
d. After the collision, both balls are moving at the same speed but in opposite directions.
e. none of the above is correct.
9. An empty railroad car of mass 1.50 !10 kg is moving with a speed of 1.20 m/s to the right
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along a track. A load of sand (0.750 !10 kg) is quickly dumped vertically downward into the
sand dumped
car as it keeps
into railroad car
moving.
as it passes
underneath
Determine the
empty railroad car
loaded railroad car
final speed of
v
the loaded
railroad car.
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a. 0.600 m/s.
b. 0.533 m/s.
c. 1.20 m/s.
-> d. 0.800 m/s.
e. 0.400 m/s.
02.27.08