# 3. Physics Practice Questions - Momentum and Energy- 84-129

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Conceptual Physics 10th Edition by Paul G. Hewitt.

### B

84. One end of a long uniform log is raised to shoulder level. Another identical log is raised at its center to the same level. Raising the second log requires about
a. the same amount of work.
b. twice as much work.
c. more than twice as much work.

### B

85. Two identical arrows, one with twice the kinetic energy of the other, are fired into a hay bale.
The faster arrow will penetrate
a. the same distance as the slower arrow.
b. twice as far as the slower arrow.
c. four times as far as the slower arrow.
d. more than four times as far as the slower arrow.
e. none of these

### D

86 . A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car
has
a. 4 times the KE.
b. 8 times the KE.
c. 12 times the KE.
d. 16 times the KE.

### A

87. A ball is projected into the air with 100 J of kinetic energy that is transformed to gravitational
potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is
a. less than 100 J.
b. more than 100 J.
c. 100 J.
d. not enough information given.

### D

88. Strictly speaking, if any electrical device in your car is turned on (such as an air conditioner,
headlights, or even a radio, more gasoline is burned by the engine. This statement is
a. totally false.
b. true only if the car's engine is running.
c. true only if the car's engine is stopped.
d. always true.
e. none of these

### A

89. A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the machine is
a. 10%.
b. 50%.
c. 90%.
d. 110%.
e. none of these

### B

90. An ungloved fist will do more damage to a jaw than a gloved fist. The reason for this is that
the ungloved fist
a. delivers a larger impulse to the jaw.
b. exerts a larger force on the jaw.
c. has less air resistance on it.
d. none of these

### A

91. A woman lifts a box from the floor. She then moves with constant speed to the other side of the
room, where she puts the box down. How much work does she do on the box while walking
across the floor at constant speed?
a. 0 J
b. more than 0 J

### E

92. A car moving at 50 km/h skids 20 m with locked brakes. How far will the car skid with locked
brakes if it is traveling at 150 km/h?
a. 20 m
b. 60m
c. 90m
d. 120m
e. 180m

### B

93. Which has greater kinetic energy, a car traveling at 30 km/h or a car of half the mass traveling
at 60 km/h?
a. the 30-km/h car
b. the 60-km/h car
c. Both have the same kinetic energy.

### D

94. A diver who weighs 500 N steps off a diving board that is 10 m above the water. The diver hits
the water with kinetic energy of
a. 10J.
b. 500 J.
c. 510 J.
d. 5000J.
e. more than 5000 J.

### C

95. Consider a hydraulic press. When the input piston is depressed 20 cm, the output piston is
observed to move 1 cm. On the same press, an input force of 1N can raise no more than
a. 1 N.
b. 10 N.
c. 20 N.
d. 21 N.

### C

96. A 2500-N pile driver ram falls 10 m and drives a post 0.1m into the ground. The average
impact force on the ram is
a. 2500 N.
b. 25,000 N.
c. 250,000N.
d. 2,500,000 N.

### E

97. A pulley system raises a 1O00-N load with 100N of input force. The efficiency of the system is
a. 10%.
b. 90%.
c. 100%.
d. 1000%.
e. not enough information given

### C

98. A jack system will increase the potential energy of a heavy load by no more than 1000Jwith a
work input of 2000 J. The efficiency of the jack system is no more than
a. 10%.
b. 20%.
c. 50%.
d. 80%.
e. not enough information given

### A

99. Which requires the most amount of work on the brakes of Ii car?
a. slowing down from 100 km/h to 70 km/h.
b. slowing down from 70 km/h to a stop.
e equal amounts for either.

### B

100. A car that travels twice as fast as another when braking to a stop will skid
a. twice as far.
b. four times as far.
c. depends on the mass of the cars

### C

101. Two identical arrows, one with twice the speed of the other, are fired into a hay bale. The
faster arrow will penetrate
a. the same distance as the slower arrow.
b. twice as far as the slower arrow.
c. four times as far as the slower arrow.
d. more than four times as far as the slower arrow.
e. none of these

### A

102. A. person on the edge of a roof throws a ball downward. It strikes the ground with 100 J of
kinetic energy. The person throws another identical ball upward with the same initial speed,
and this too falls to the ground. Neglecting air resistance, the second ball hits the ground with
a kinetic energy of
a. 100 J.
b. 200 J.
c. less than 100 J.
d. more than 200 J.
e. none of these

### D

103. If a power plant is 30% efficient, and the transmission system that delivers power to consumers
is 60%efficient, then the overall efficiency is
a. 90%.
b. 60%.
c. 30%.
d. 18%.
e. none of these

### D

104 How many joules of energy are in 1 kWh?
a. 1 J
b. 60 J
c. 60 kJ
d. 3.6MJ
e. none of these

### D

105 a. car's engines is 20% efficient. When cruising, the car encounters an average retarding force
of 1000 N. If the energy content of gasoline is 40 MJ/ L, how many kilometers per liter does the
car get?
a. 14 km/L
b. 12 km/L
c. 10 km/L
d. 8 km/L
e. none of these

### B

106 Suppose a miracle car has a 100% efficient engine and burns fuel that has a 40 MJ/L energy
content. If the air drag and overall frictional forces on this car traveling at highway speeds is
1000 N, what is the overall limit in distance per liter it could be driven on the highway?
a. 30 km
b. 40 km
c. 50 km
d. more than 50 km
e. not enough information

### B

107 a. flower pot of mass m falls from rest to the ground below, a distance h. Which statement is correct?
a. The speed of the pot when it hits the ground is proportional to h.
b. The Ke. of the pot when it hits the ground is proportional to h.
c. The Ke. of the pot when it hits the ground does not depend on m.
0 The speed of the pot when it hits the ground depends on m.
e. None of these are correct.

### C

108. A toy cart moves with a kinetic energy of 40 J. If it moves with twice the speed, its kinetic
energy will be
a. 40 J.
b. 80 J.
c. 160 J.
d. unknown unless we know the mass of the cart.

### A

109 Whereas impulse involves the time that a force acts, work involves the
a. distance that a force acts.
b. time and distance that a force acts.
c. acceleration that a force produces.

### A

110 When a rifle is fired, it recoils so both the bullet and rifle are set in motion.
ideally acquire equal
a. but opposite amounts of momentum.
b. amounts of kinetic energy.
c. both of these
d. none of these
e.The rifle and bullet

### E

111 a. moving object has
a. speed.
b. velocity.
c. momentum.
d. energy.
e. all of these

### A

112 What does an object have when moving that it doesn't have when at rest?
a. momentum
b. energy
c. mass
d. inertia
e. none of these

### B

113 If an object has kinetic energy, then it also must have
a. impulse.
b. momentum.
c. acceleration.
d. force.
e. none of these

### A

114 If the speed of a moving object doubles, then what else doubles?
a. momentum
b. kinetic energy
c. acceleration
d. all of these
e. none of these

### C

115. An object at rest may have
a. speed.
b. velocity.
c. energy.
d. momentum.
e. none of these

### C

116. A feather and a coin dropped in a vacuum fall with equal
a. forces.
b. momenta.
c. accelerations.
d. kinetic energies.
e. none of these

### E

117. A heavy and a light object released from the same height in a vacuum have equal
a. weights.
b. momenta.
c. energies.
d. all of these
e. none of these

### B

118. Two pool balls, each moving at 2m/ s, roll toward each other and collide. Suppose after
bouncing apart, each moves at 4 m/ s. This collision violates conservation of
a. momentum.
b. kinetic energy.
c. both of these
d. none of these

### B

119. Compared to a recoiling rifle, the bullet fired has a greater
a. momentum.
b. kinetic energy.
c. none of these

### B

120. In bungee jumping, the change in a jumper's kinetic energy equals the average force of the
bungee cord multiplied by the stretching
a. time.
b. distance.
c. both of these
d. none of these

### B

121. The reason a bullet has more kinetic energy than the recoiling rifle from which it is fired is
because the force on the bullet acts over a longer
a. time.
b. distance.
c. both of these
d. neither of these

### B

122. An open freight car rolls friction-free along a horizontal track in a pouring rain that falls
vertically. As water accumulates in the car, its speed
a. increases.
b. decreases.
c. doesn't change.

### C

123. A car has a head-on collision with another car of the same momentum. An identical car
driving with the same speed as the first car runs into an enormously massive wall. The
greatest impulse will occur on the car that is in the collision with the
a. approaching car.
b. the wall.
c. Both impulses will be the same.

### A

124. A golf ball is thrown at and bounces backward from a massive bowling ball that is initially at
rest. After the collision, compared to the golf ball, the bowling ball has more
a. momentum, but less kinetic energy.
b. kinetic energy, but less momentum.
c. momentum and more kinetic energy.
d. but it has less momentum and less kinetic energy.
e. Not enough information is given to say.

### B

125. A popular swinging-balls apparatus consists of an aligned row of identical elastic balls that are suspended by strings so they barely touch each other. When two balls are lifted from one end and released, they strike the row and two balls pop out from the other end. lf instead one ball popped out with twice the speed of the two, this would be a violation of conservation of
a. momentum.
b. energy.
c. both of these
d. none of these

### C

126. A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces stuck together after the collision is the same as it was before the collision, but this is not true of the kinetic energy, which is partly turned into heat. What percentage of the kinetic energy is turned into heat?
a. 0 %
b. 25%
c. 50%
d. 75%
e. not enough information given

### A

127. Two identical freight cars roll without friction towards each other on a level track. One rolls at 2 m/s and the other rolls at 1 m/s. After the cars collide, they couple and roll together with a speed of
a. 0.5 m/s.
b. 0.33 ml s.
c. 0.67 m/s.
d. 1.0 m/s.
e. none of these

### E

128. A 1-kg ball dropped from a height of 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about
a. 0.5 J.
b. 1.0 J.
c. 1.5 J.
d. 2.0 J.
e. more than 2.0 J.

### B

129. A sandbag in outer space moves at 3 m/ s and collides and sticks to a half-as-massive sandbag
initially at rest. Compared with the kinetic energy of the moving bag before collision, the
kinetic energy of the coupled bags after collision is
a. one-third.
b. two-thirds.
c. three-quarters.
d. not enough information to say

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