Download Work and Energy MC

Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Person X pushes twice as hard against a stationary brick wall as person Y. Which one
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of the following statements is correct?
A) Both do positive work, but person X does twice the work of person Y.
B) Both do positive work, but person X does four times the work of person Y.
C) Both do zero work.
D) Both do positive work, but person X does one-half the work of person Y.
E) Both do the same amount of positive work.
2) Two men, Joel and Jerry, push against a car that has stalled, trying unsuccessfully to get
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it moving. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer.
Compare the work they do on the car.
A) Joel does 75% more work than Jerry.
B) Joel does 25% more work than Jerry.
C) Jerry does 50% more work than Joel.
D) Joel does 50% more work than Jerry.
E) Neither of them does any work.
3) If the force exerted on an object is in the negative direction, the work it does on the
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object must be
A) negative.
B) positive.
C) The work could be either positive or negative, depending on the direction the
object moves.
4) A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original
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position. How much work did the gravitational force exerted by Earth on the object do
on the bucket during this process?
A) 90 J
B) 180 J
C) 900 J
D) 45 J
E) 0 J
5) You throw a baseball straight up. Compare the sign of the work done by the
gravitational force exerted by Earth on the object while the ball goes up with the sign of
the work done by the same force while it goes down.
A) The work is positive on the way up and positive on the way down.
B) The work is negative on the way up and positive on the way down.
C) The work is positive on the way up and negative on the way down.
D) The work is negative on the way up and on the way down because gravity is
always downward.
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6) Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg
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object moving at 20 m/s?
A) the 1000-kg object
B) the 500-kg object
C) Both have the same kinetic energy.
7) A truck has four times the mass of a car and is moving with twice the speed of the car.
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If K t and Kc refer to the kinetic energies of truck and car respectively, it is correct to
say that
A) K t = K c.
B) K t = 2K c.
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C) K t = Kc.
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D) K t = 16K c.
E) K t = 4K c.
8) Three cars (car F, car G, and car H) are moving with the same speed and slam on their
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brakes. The most massive car is car F, and the least massive is car H. If the tires of all
three cars have identical coefficients of kinetic friction with the road surface, which car
travels the longest distance to skid to a stop?
A) They all travel the same distance in stopping.
B) car G
C) car F
D) car H
9) Three cars (car L, car M, and car N) are moving with the same speed and slam on their
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brakes. The most massive car is car L, and the least massive is car N. If the tires of all
three cars have identical coefficients of kinetic friction with the road surface, for which
car is the amount of work done by friction in stopping it the greatest?
A) The amount of work done by friction is the same for all cars.
B) car L
C) car N
D) car M
10) A 4.0 kg object is moving with speed 2.0 m/s. A 1.0 kg object is moving with speed
4.0 m/s. The same stopping force is exerted on both objects and both objects are
brought to rest. Which object travels the greater distance before stopping?
A) the 1.0 kg object
B) the 4.0 kg object
C) Both objects travel the same distance.
D) It cannot be determined from the information given.
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11) You slam on the brakes of your car in a panic, and skid a certain distance on a straight
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level road. If you had been traveling twice as fast, what distance would the car have
skidded, under the same conditions?
A) It would have skidded 4 times farther.
B) It would have skidded 1.4 times farther.
C) It would have skidded one half as far.
D) It would have skidded twice as far.
E) It is impossible to tell from the information given.
12) Which requires more work, increasing a car's speed from 0 mph to 30 mph or from 50
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mph to 60 mph?
A) 0 mph to 30 mph
B) 50 mph to 60 mph
C) It is the same in both cases.
13) A stone is held at a height h above the ground. A second stone with four times the
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mass of the first one is held at the same height. The gravitational potential energy of
the second stone-Earth system compared to that of the first stone-Earth system is
A) one-half as much.
B) the same.
C) twice as much.
D) four times as much.
E) one-fourth as much.
14) You and your friend, who has the same mass as you, want to go to the top of the Eiffel
Tower. Your friend takes the elevator straight up. You decide to walk up the spiral
stairway, taking longer to do so. Compare the gravitational potential energy of the
system you-Earth and your friend-Earth, after you both reach the top.
A) It is impossible to tell, since the times you both took are unknown.
B) The you-Earth system's gravitational potential energy is greater than the
friend-Earth system, because you traveled a greater distance in getting to the top.
C) The friend-Earth system's gravitational potential energy is greater than the
you-Earth system's gravitational potential energy, because he got to the top faster.
D) It is impossible to tell, since the distances you both traveled are unknown.
E) Both systems have the same amount of gravitational potential energy at the top.
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15) The graphs shown show the magnitude F of the force exerted by a spring as a function
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of the distance x the spring has been stretched. For which one of the graphs does the
spring obey Hooke's law?
A)
graph a
B) graph
b
C)
graph c
D)
graph d
E) graph
e
16) A heavy dart and a light dart are launched horizontally on a frictionless table by
identical ideal springs. Both springs were initially compressed by the same amount.
Which of the following statements about these darts are correct? (There could be more
than one correct choice.)
A) The lighter dart leaves the spring moving faster than the heavy dart.
B) The darts both have the same kinetic energy just as they move free of the spring.
C) The heavy dart had more initial elastic potential energy than the light dart.
D) Both darts had the same initial elastic potential energy.
E) Both darts move free of the spring with the same speed.
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17) When you throw a pebble straight up with initial speed V, it reaches a maximum height
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H assuming there is no air resistance. At what speed should you throw it up vertically
so it will go twice as high?
A) 8V
B) 2 V
C) 4V
D) 16V
E) 2V
18) When you drop a pebble from height H, it reaches the ground with speed V assuming
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there is no air resistance. From what height should you drop it so it will reach the
ground with twice speed?
A) 8H
B) 16H
C) 2H
D) 2H
E) 4H
19) When you drop a pebble from height H, it reaches the ground with kinetic energy K
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assuming there is no air resistance. From what height should you drop it so it will reach
the ground with twice as much kinetic energy?
A) 2 H
B) 2H
C) 8H
D) 16H
E) 4H
20) Two objects, one of mass m and the other of mass 2m, are dropped from the top of a
building. Assuming there is no air resistance, when they hit the ground
A) the heavier one will have four times the kinetic energy of the lighter one.
B) the heavier one will have one-fourth the kinetic energy of the lighter one.
C) the heavier one will have twice the kinetic energy of the lighter one.
D) the heavier one will have half the kinetic energy of the lighter one.
E) both will have the same kinetic energy.
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21) Swimmers at a water park have a choice of two frictionless water slides, as shown in
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the figure. Although both slides drop over the same height h, slide 1 is straight while
slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1
of a swimmer reaching the bottom of slide 1 compare with v2, the speed of a swimmer
reaching the end of slide 2?
A) v1 < v 2
B) v1 = v 2
C) v1 > v 2
D) The heavier swimmer will have a greater speed than the lighter swimmer, no
matter which slide he uses.
E) No simple relationship exists between v1 and v2.
22) Two frisky otters slide down frictionless hillsides of the same height but different
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slopes. The slope of the hill of otter 1 is 30°, while the slope of the hill of otter 2 is 60°.
If both start from rest, which otter is moving faster when she reaches the bottom of her
hill?
A) The otter that took the shorter time is moving faster.
B) The heavier otter is moving faster, no matter which hill she used.
C) Otter 1 is moving faster.
D) Both otters have the same speed at the bottom.
E) Otter 2 is moving faster.
23) A lightweight object and a very heavy object are sliding with equal speeds along a level
frictionless surface. They both slide up the same frictionless hill with no air resistance.
Which object rises to a greater height?
A) They both slide to exactly the same height.
B) The lightweight object, because the gravitational force exerted on it is less.
C) The heavy object, because it has more mass to carry it up the hill.
D) The heavy object, because it has greater initial kinetic energy.
E) The light object, because gravity slows it down less.
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24) A person stands on the edge of a cliff. She throws three identical rocks with the same
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speed. Rock X is thrown vertically upward, rock Y is thrown horizontally, and rock Z is
thrown vertically downward. If the ground at the base of the cliff is level, which rock
hits the ground with the greatest speed if there is no air resistance?
A) rock Y
B) rock X
C) rock Z
D) They all hit the ground with the same speed.
25) Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial
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speed twice as high as Bill. Assuming there is no air resistance, the maximum height of
Joe's ball will be
A) roughly 1.4 times that of Bill's ball.
B) eight times that of Bill's ball.
C) two times that of Bill's ball.
D) four times that of Bill's ball.
E) equal to that of Bill's ball.
26) A stone can slide down one of four different frictionless ramps, as shown in the figure.
For which ramp will the speed of the ball be the greatest at the bottom?
A)
ramp Z
B) ramp Y
C) ramp X
D) The speed of the ball will be the same for all ramps.
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27) A girl throws a stone from a bridge. Consider the following ways she might throw the
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stone. The speed of the stone as it leaves her hand is the same in each case.
Case A:
Case B:
Case C:
Case D:
Thrown straight up.
Thrown straight down.
Thrown out at an angle of 45° above horizontal.
Thrown straight out horizontally.
In which case will the speed of the stone be greatest when it hits the water below if
there is no significant air resistance?
A) Case A
B) Case B
C) Case C
D) Case D
E) The speed will be the same in all cases.
28) A heavy frog and a light frog jump straight up. They push off in such a way that they
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both have the same kinetic energy just as they leave the ground. Assume air resistance
is negligible. Which of the following statements about these frogs are correct? (There
could be more than one correct choice.)
A) The lighter frog goes higher than the heavier frog.
B) Just as they leave the ground, the heavier frog is moving faster than the lighter
frog.
C) They both leave the ground with the same speed.
D) The heavier frog goes higher than the lighter frog.
E) Just as they leave the ground, the lighter frog is moving faster than the heavier
frog.
F) Both frogs reach the same maximum height.
29) Two identical grasshoppers jump with the same initial speed. Grasshopper A goes
straight up, but grasshopper B goes up at a 66° angle above the horizontal. Assume no
air resistance and choose your system to be grasshopper-Earth. Which of the following
statements about these grasshoppers are correct? (There could be more than one correct
choice.)
A) At their highest point, both systems have the same amount of gravitational
potential energy.
B) At their highest point, both systems have the same amount of kinetic energy.
C) At their highest point, grasshopper B is moving faster than grasshopper A.
D) At their highest point, both systems have the same amount of mechanical energy.
E) At their highest point, the system grasshopper A-Earth has more gravitational
potential energy than the system grasshopper B-Earth.
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30) A heavy rock and a light rock are dropped from the same height. The forces exerted on
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them by air are negligible. Which of the following statements about these rocks are
correct? (There could be more than one correct choice.)
A) Both rocks have the same speed when they reach the ground.
B) When they reach the ground, the heavier rock has more kinetic energy than the
lighter rock.
C) Both rocks have the same kinetic energy when they reach the ground.
D) The heavier rock reaches the ground before the lighter rock.
E) Just as they were released, the two systems consisting of each rock and Earth had
the same amount of gravitational potential energy.
31) A heavy stone and a light stone are released from rest in such a way that the amount of
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gravitational potential energy of the system rock-Earth for each rock is the same just as
they are released. Air resistance is negligibly small. Which of the following statements
about these stones are correct? (There could be more than one correct choice.)
A) The stones both have the same speed just as they reach the ground.
B) The stones both have the same kinetic energy just as they reach the ground.
C) The initial height of the light stone is greater than the initial height of the heavy
stone.
D) The stones must have been released from the same height.
E) Just as it reaches the ground, the light stone is traveling faster than the heavy
stone.
32) A 1-kg ball is released from a height of 6 m, and a 2-kg ball is released from a height of
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3 m. Air resistance is negligible as they fall. Which of the following statements about
these balls are correct? (There could be more than one correct choice.)
A) Both balls will take the same time to reach the ground.
B) As they reach the ground, the 1-kg ball will have more kinetic energy than the
2-kg ball because it was dropped from a greater height.
C) Both balls will reach the ground with the same kinetic energy.
D) As they reach the ground, the 1-kg ball will be moving faster than the 2-kg ball.
E) Both balls will reach the ground with the same speed.
33) A heavy dart and a light dart are launched vertically by identical ideal springs. Both
springs were initially compressed by the same amount. There is no significant air
resistance. Which of the following statements about these darts are correct? (There
could be more than one correct choice.)
A) The light dart goes higher than the heavy dart.
B) At the maximum height, the systems consisting of each dart and Earth have the
same gravitational potential energy.
C) Both darts began moving upward with the same initial speed.
D) Both darts reach the same maximum height.
E) The heavy dart goes higher than the light dart.
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34) A heavy sled and a light sled, both moving horizontally with the same speed, suddenly
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slide onto a rough patch of snow and eventually come to a stop. The coefficient of
kinetic friction between the sleds and the rough snow is the same for both of them.
Which of the following statements about these sleds are correct? (There could be more
than one correct choice.)
A) Both sleds will slide the same distance on the rough snow before stopping.
B) The friction force exerted on the sled by the snow will do more negative work on
the heavy sled than on the light sled.
C) The heavy sled will slide farther on the rough snow than the light sled.
D) The friction force exerted on the sled by the snow will do the same amount of
work on both sleds.
E) The light sled will slide farther on the rough snow than the heavy sled.
35) A heavy sled and a light sled, both moving horizontally with the same kinetic energy,
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suddenly slide onto a rough patch of snow and eventually come to a stop. The
coefficient of kinetic friction between the sleds and the rough snow is the same for both
of them. Which of the following statements about these sleds are correct? (There could
be more than one correct choice.)
A) The light sled will slide farther on the rough snow than the heavy sled.
B) The heavy sled will slide farther on the rough snow than the light sled.
C) On the rough snow, the change in kinetic energy will be the same for both sleds.
D) Both sleds will slide the same distance on the rough snow before stopping.
E) The friction force exerted on the sleds by the snow will do the same amount of
work on both sleds.
36) If a stone is dropped so that the initial gravitational potential energy of the system
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stone-Earth is 100 J but it reaches the ground with a kinetic energy of only 75 J, this is
a violation of the principle of conservation of energy.
A) True
B) False
37) If the units of your answer are kg m2/s3, which of the following types of quantities
could your answer be? (There could be more than one correct choice.)
A) work
B) force
C) power
D) kinetic energy
E) potential energy
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38) Two cyclists who weigh the same and have identical bicycles ride up the same
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mountain, both starting at the same time. Joe rides straight up the mountain, and Bob
rides up the longer road that has a lower grade. Joe gets to the top before Bob. Ignoring
friction and wind resistance, which one of the following statements is true?
A) The amount of internal energy converted to gravitational potential energy of the
system Joe- Earth is equal to the amount of internal energy converted to
gravitational potential energy of the system Bob-Earth, but the average power of
the process for Joe is greater than that for Bob.
B) The average power of the process for Bob and Joe was the same, but Joe converted
more of the internal energy into the gravitational potential energy in getting there.
C) Bob and Joe converted the same amount of internal energy to gravitational
potential energy, and the average power of the process for each cyclist was also the
same.
D) The amount of internal energy converted to gravitational potential energy of the
system Joe- Earth is greater than the amount of internal energy converted to
gravitational potential energy of the system Bob-Earth, and the average power of
the process for Joe is greater than that for Bob.
39) A force is exerted on a system doing work W in a time T. What will be the power of the
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process that involves a force that does six times as much work in half as much time?
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1
P
A)
B) P
C) P
D) 6P
E) 12P
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40) The
momentum of an isolated system is conserved
A) in both elastic and inelastic collisions.
B) only in elastic collisions.
C) only in inelastic collisions.
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41) In
an inelastic collision involving an isolated system, the final total momentum is
A) less than the initial momentum.
B) more than the initial momentum.
C) exactly the same as the initial momentum.
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42) A 5-kg ball collides inelastically head-on with a 10-kg ball, which is initially stationary.
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Which of the following statements is true? (There could be more than one correct
choice.)
A) The magnitude of the change of velocity the 5-kg ball experiences is greater than
that of the 10-kg ball.
B) The magnitude of the change of the momentum of the 5-kg ball is equal to the
magnitude of the change of momentum of the 10-kg ball.
C) The magnitude of the change of velocity the 5-kg ball experiences is equal to that
of the 10-kg ball.
D) Both balls lose all their momentum since the collision is inelastic.
E) The magnitude of the change of velocity the 5-kg ball experiences is less than that
of the 10-kg ball.
43) In a game of pool, the white cue ball hits the #5 ball and stops, while the #5 ball moves
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away with the same velocity as the cue ball had originally. Both balls have the same
mass. This type of collision is
A) elastic.
B) completely inelastic.
C) somewhat inelastic.
44) In the figure, determine the character of the collision. The masses of the blocks, and the
velocities before and after, are shown. The collision is
A)
partially inelastic.
B) not possible because momentum is not conserved.
C) completely inelastic.
D) perfectly elastic.
E) characterized by an increase in kinetic energy.
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45) In the figure showing an isolated system, determine the character of the collision. The
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masses of the blocks, and the velocities before and after, are shown. The collision is
A)
partially inelastic.
B) characterized by an increase in kinetic energy.
C) not possible because momentum is not conserved.
D) perfectly elastic.
E) completely inelastic.
46) In the figure, determine the character of the collision. The masses of the blocks, and the
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velocities before and after, are shown. The collision is
A)
characterized by an increase in kinetic energy.
B) completely inelastic.
C) partially inelastic.
D) perfectly elastic.
E) not possible because momentum is not conserved.
47) An
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48) If a quantity you calculated had units of kg m/s, what type of quantity could it be?
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egg falls from a bird's nest in a tree and feels no effects due to the air. As it falls,
A) both its mechanical energy and its momentum are conserved.
B) only its mechanical energy is conserved.
C) both its kinetic energy and its momentum are conserved.
D) only its kinetic energy is conserved.
E) only its momentum is conserved.
(There could be more than one correct choice.)
A) impulse
B) force
C) momentum
D) work
E) kinetic energy
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49) A railroad car collides with and sticks to an identical railroad car that is initially at rest.
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After the collision, the kinetic energy of the system
A) is half as much as before.
B) is the same as before.
C) is one third as much as before.
D) is one fourth as much as before.
E) is one quarter as much as before.
50) A rubber ball bounces off of a wall with an initial speed v and reverses its direction so
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its speed is v right after the bounce. As a result of this bounce, which of the following
quantities of the ball are conserved? (There could be more than one correct choice.)
A) the kinetic energy of the ball
B) both the momentum and the kinetic energy of the ball
C) the momentum of the ball
D) None of the above quantities are conserved.
51) On a horizontal frictionless air table, a puck runs into an ideal horizontal spring that is
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fastened to the table. The puck compresses the spring by 15 cm before coming to rest.
During the compression process, which quantities are conserved?
A) only the momentum of the puck
B) only the kinetic energy of the puck
C) the momentum and the kinetic energy of the puck
D) the momentum and the mechanical energy of the puck
E) only the mechanical energy (kinetic plus potential) of the puck
52) Two objects of different mass have equal, non-zero kinetic energies. Which object has
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the greater magnitude momentum?
A) the heavier object
B) the lighter object
C) They both have the same magnitude momentum.
53) Two objects of different masses have momentum of equal, non-zero magnitude. Which
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object has more kinetic energy?
A) the lighter object
B) the heavier object
C) They both have the same kinetic energy.
54) If you want to double the kinetic energy of a gas molecule, by what factor must you
increase its momentum?
A) 4
B) 2 2
C)
D)
2
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E)
55) If you want to double the momentum of a gas molecule, by what factor must you
increase its kinetic energy?
A) 2
B) 2 2
C)
D)
2
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16
E) 4
54)
2
55)
56) A firecracker explodes in midair and breaks up into many fragments. Which of the
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following statements are true regarding conditions immediately before and immediately
after the explosion:
I. The total momentum of the fragments is equal to the original momentum of the
firecracker.
II. The total kinetic energy of the fragments is equal to the original kinetic energy of the
firecracker.
A)
B) Statement II only
Statement I only
C) Both Statement I and Statement II
D)
Neither statement is true.
57) How do the escape speeds for two rockets, the first weighing 20 N and the second
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weighing 20,000 N compare?
A) The escape speed for the lighter rocket is smaller than that for the heavier rocket.
B) The escape speed for the lighter rocket is greater than that for the heavier rocket.
C) The escape speed for the lighter rocket is the same as that for the heavier rocket.
58) Planet A has twice the mass of Planet B. From this information, what can we conclude
about the escape speed for Planet A compared to that of Planet B?
A) The escape speed for Planet A must be twice as great as the escape speed from
Planet B.
B) The escape speed for Planet A is the same as the escape speed from Planet B.
C) The escape speed for Planet A is greater than the escape speed from Planet B, but
we cannot say how much greater.
D) The escape speed for Planet A must be four times as great as the escape speed
from Planet B.
E) We cannot conclude anything about the escape speed for Planet A without
knowing the radii of the two planets.
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58)
Answer Key
Testname: UNTITLED2
1) C
2) E
3) C
4) E
5) B
6) B
7) D
8) A
9) B
10) C
11) A
12) B
13) D
14) E
15) B
16) A, B, D
17) B
18) E
19) B
20) C
21) B
22) D
23) A
24) D
25) D
26) D
27) E
28) E, F
29) C, D, E
30) A, B
31) B, C, E
32) C, D
33) A, B
34) A, B
35) A, C, E
36) B
37) C
38) A
39) E
40) A
41) C
42) A, B
43) A
44) D
45) C
46) B
47) B
48) A, C
49) A
50) A
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Answer Key
Testname: UNTITLED2
51) E
52) A
53) A
54) E
55) E
56) A
57) C
58) E
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