Download Modified True/False Indicate whether the sentence or statement is

Modified True/False
Indicate whether the sentence or statement is true or false. If false, change the identified word or phrase to make the
sentence or statement true.
____
1. Linear momentum is a scalar quantity. _________________________
____
2. The impulse is always in the same direction as the net force. _________________________
____
3. The average force accurately represents the actual force during a collision.
______________________________
____
4. If the net force acting on a system of objects is zero, the linear momentum of the system is conserved for any
number of objects. _________________________
____
5. In a one-dimensional linear momentum question, only the speed is important to know for colliding objects.
______________________________
____
6. Momentum is not conserved in all collisions. _________________________
____
7. The direction of the net force and the direction of the impulse are always the same.
_________________________
____
8. A single train car loaded with sand travels by itself along a horizontal frictionless track at a constant speed. A
hole is punctured in the bottom of train and the sand slowly leaks out causing the train car to speed up.
_________________________
____
9. Two blocks of different mass are attached by a string and slide along a horizontal frictionless surface at a
constant speed. When the string is cut, the speed of the larger block will stay the same.
_________________________
____ 10. A system consists of a sliding wooden block on a wooden plank. The plank is mounted on frictionless wheels.
Friction causes the block to slow down and stop, so momentum of the system is not conserved.
_________________________
____ 11. It is possible that an object can receive a larger impulse from a small force than from a large force.
_________________________
____ 12. During a collision of a bullet and a wooden block, the force of friction can be neglected because the interaction
is so brief. _________________________
____ 13. When you triple the velocity of an object of constant mass, you also triple the momentum.
_________________________
____ 14. Momentum cannot be used during car collisions that involve cars with “crumple zones.”
_________________________
____ 15. Knowledge of momentum has not reduced the number of deaths in vehicular accidents in the past 10 years.
_________________________
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
____ 16. A 5.0-kg cat travelling at 1.3 m/s [E] has a momentum of
a. 6.5 m/s [E]
d. 3.8 m/s [W]
b. 6.5 m/s [W]
e. none of the above
c. 3.8 m/s [E]
____ 17. A bobsleigh and its riders have a combined mass of 598 kg. They cross the finish line with a velocity of 125
km/h [forward]. The momentum of the team and the bobsleigh at the finish line is
a. 4.78 kg⋅m/s [forward]
d. 7.48 × 104 kg⋅m/s [forward]
b. 17.2 kg⋅m/s [forward]
e. 2.69 × 105 kg⋅m/s [forward]
4
c. 2.08 × 10 kg⋅m/s [forward]
____ 18. A bullet with a momentum of 2.8 kg⋅m/s [E] is travelling at a speed of 187 m/s. The mass of the bullet is
a. 0.015 g
d. 67 g
b. 0.067 g
e. not enough information
c. 15 g
____ 19. During collisions, it is often acceptable to ignore the force of gravity on an object. This is because
a. the time the other forces act is so short that we can ignore the force of gravity
b. the force of gravity is always acting on the object and we only consider change
c. the object may be in space and the gravitational force does not exist
d. the collision is often perpendicular to the force of gravity, so Fg does not play a role
e. the force of gravity is insignificant compared to the other forces acting on the object
____ 20. A net force of 12 N changes the momentum of a 250-g ball by 3.7 kg⋅m/s. The force acts for
a. 0.31 s
d. 3.2 s
b. 0.81 s
e. 44 s
c. 1.2 s
____ 21. A 2200 kg car starts from rest and speeds up to 12 m/s in 5.2 s. The net force acting on the car is
a. 1.8 × 102 N
d. 5.1 × 103 N
2
b. 4.2 × 10 N
e. 1.4 × 105 N
4
c. 1.1 × 10 N
____ 22. A car with a mass of 1800 kg slows from 42 km/h [E] to 28 km/h [E]. The impulse from the brakes is
a. 2.5 × 104 N⋅s [E]
d. 2.1 × 104 N⋅s [W]
b. 2.5 × 104 N⋅s [W]
e. 7.0 × 103 N⋅s [W]
4
c. 2.1 ×10 N⋅s [E]
____ 23. A 1.5-kg bird is flying at a velocity of 18 m/s [22º above the horizontal]. The vertical component of its
momentum is
a. 10 m/s [up] (2 significant digits)
d. 17 m/s [up]
b. 6.7 kg⋅m/s [up]
e. none of the above
c. 25 kg⋅m/s [up]
____ 24. A 1.5-kg bird is flying west at a velocity of 18 m/s [22º above the horizontal]. The horizontal component of its
momentum is
a. 10 m/s [W] (2 significant digits)
d. 17 m/s [W]
b. 6.7 kg⋅m/s [W]
e. 17 kg⋅m/s [E]
c. 25 kg⋅m/s [W]
____ 25. A bullet with a mass of 28 g is fired from a 2.8-kg gun that is stationary, but free to recoil. After the bullet is
fired, the gun is observed to be moving at 1.4 m/s [left]. The velocity of the bullet is
a. 140 m/s [left]
d. 71 m/s [left]
b. 140 m/s [right]
e. 71 m/s
c. 71 m/s [right]
____ 26. A shell is fired from a gun mounted on a battleship. Which of the following statement is NOT true?
a. There will be a force to push the boat in the opposite direction of the shell.
b. The recoil spring on the barrel is to minimize the force on the deck of the ship.
c. Neglecting fluid friction, the momentum of the boat and shell have the same magnitude.
d. To calculate the speed of the boat we would need to know the recoil length of the gun.
e. A larger mass of shell will increase the recoil force felt by the ship.
____ 27. A person jumps from an airplane and reaches terminal speed.
a. The momentum of the jumper is constant because there is no external net force.
b. The momentum of the person–Earth system is not conserved because of air friction.
c. When the chute is opened, the force disrupts the conservation of momentum of the
person–Earth system.
d. two of A, B, and C are correct
e. all of A, B, and C are correct
____ 28. An arrow slows down from 43 m/s to 28 m/s as it passes through an apple. If the 493-g apple was originally at
rest and sped up to 0.44 m/s, the mass of the arrow is
a. 5.0 g
d. 29 g
b. 7.7 g
e. 7.7 kg
c. 14 g
____ 29. A boy throws a 15-kg ball at 4.7 m/s to a 65-kg girl who is stationary and standing on a skateboard. After
catching the ball, the girl is travelling at
a. 0 m/s
d. 3.2 m/s
b. 0.88 m/s
e. 4.7 m/s
c. 1.1 m/s
____ 30. A goalie standing on a frictionless surface catches a 270.0-g puck travelling at 95.0 km/h. After catching the
puck, the goalie is moving at 8.90 cm/s. The mass of the goalie (including equipment) is
a. 75.2 kg
d. 84.2 kg
b. 79.8 kg
e. 91.7 kg
c. 80.1 kg
____ 31. A 55-kg person carrying a 5.0-kg ball slides along a horizontal frictionless surface. He tosses the ball
perpendicular to his direction of travel relative to himself.
a. His path will not change.
b. The ball will have a smaller angle from the original path than he will.
c. His speed does not change.
d. He speeds up.
e. He slows down.
____ 32. A 55-kg person carrying a 5.0-kg ball slides along a horizontal frictionless surface. He tosses the ball forward.
a. His path will not change.
b. The ball will have a smaller angle from the original path than he will.
c. His speed does not change.
d. He speeds up.
e. He will most likely stop moving forward.
____ 33. A moving curling stone, A, collides head on with a stationary stone, B. Both stones are of identical mass. If
friction is negligible during this linear elastic collision,
a. stone A will slow down
b. after the collision, the momentum of stone B will be less than that of stone A
c. both stones will come to rest shortly after the collision
d. after the collision, the kinetic energy of the stone B will be less than that of stone A
e. after the collision, stone A will have a speed of zero
____ 34. If an arrow’s mass is doubled and the speed is halved, the momentum is changed by a factor of
a. 0.25
d. 2
b. 0.5
e. 4
c. 1
____ 35. A car (of constant mass) doubles its speed while driving up a hill sloped at 45º. The factor by which its
momentum changes is
a. 0
d. 3
____ 36.
____ 37.
____ 38.
____ 39.
____ 40.
____ 41.
____ 42.
____ 43.
b. 1
e. 4
c. 2
A car (of constant mass) doubles its kinetic energy while driving down a hill sloped at 45º. The factor by which
its momentum changes is
a. 1
d. 2.8
b. 1.4
e. 4
c. 2
A ball rolling down a hill doubles its speed but reduces its gravitational energy to one-fifth its starting value.
The factor by which its momentum changes is
a. 0.4
d. 2
b. 1
e. 10
c. 1.4
A ball rolling down a hill doubles its momentum but reduces its gravitational energy to one-third its starting
value. The factor by which its kinetic energy changes is
a. 0.66
d. 4
b. 1
e. 6
c. 2
A 72-kg girl on a skateboard doubles her kinetic energy coasting down a hill.
a. Momentum is conserved.
b. The increase in kinetic energy is offset by a decrease in momentum.
c. The momentum will also double.
d. Her momentum does not change.
e. none of the above
A sabotaged curling stone explodes into three pieces as it travels across the ice. Neglecting the force of friction,
a. all three pieces will travel at the same speed
b. the magnitudes of the momenta for each piece will be the same
c. an external net force had to act on the stone to accelerate the three pieces
d. the components perpendicular to the original motion must add up to zero
e. momentum is not conserved because of the small explosive charge
Two young sisters with a combined mass of 75 kg ride on a cart of mass 30.0 kg travelling at 2.0 m/s. If they
jump off together so they land with zero speed relative to the ground, the change in speed of the cart is
a. 0 m/s
d. 5.0 m/s
b. 2.0 m/s
e. 7.0 m/s
c. 4.0 m/s
A force of 4.0 N [S] is applied to a 2.0-kg block sliding west at 3.0 m/s on a smooth surface. The puck will be
moving exactly south-west after
a. 1.1 s
d. 2.8 s
b. 1.5 s
e. 4.2 s
c. 2.1 s
A woman of mass M is at rest on a frictionless skateboard of negligible mass. She throws a cement block of
mass m with a velocity v relative to the ground. After the throw, her velocity relative to the ground is
a. –mv
d. Mv
b.
e.
c.
____ 44. A two-dimensional collision occurs as shown below.
Which vector below most closely represents the new velocity of P?
a. A
d. D
b. B
e. E
c. C
____ 45. Two objects of equal mass with the speeds indicated by the vectors below, collide and stick together.
Which vector below best represents the velocity of the combined objects after the collision?
a. A
d. D
b. B
e. E
c. C
____ 46. To compare the kinetic energies of two objects, you must know
a. their masses
d. the forces acting on them
b. their velocities
e. the work done to stop each of them
c. their momenta
____ 47. When you catch a fast-moving baseball, your hand hurts less if you move it in the direction of the ball because
a. the ball changes momentum more slowly
b. the force applied is smaller
c. you decrease the impulse required to stop the ball
d. two of A, B, and C
e. all of A, B, and C
____ 48. When a baseball bounces on the ground
a. momentum is conserved in the Earth–ball system
b. the impulse is the same as if the baseball landed without bouncing
c. it leaves the surface with the same speed that it impacted the surface with
d. kinetic energy is imparted to the ground
e. the force applied by the surface is smaller than if it didn't bounce
____ 49. Two objects strike a glancing blow. The diagram below shows the momenta of some of the objects are shown
before and after the collision.
Which vector best represents the momentum of object P after the collision?
a. A
d. D
b. B
e. E
c. C
____ 50. A gun is mounted on a wooden plank. The plank is stationary and is mounted on frictionless wheels. A heavy
wooden block is set in front of the gun, and the gun is fired into the wooden block, which then slows to a stop
due to friction between the block and the plank.
a. The plank does not move.
b. Momentum is not conserved because of the frictional force.
c. The speed of the plank is zero immediately after the collision between the bullet and block.
d. The plank will have shifted position relative to its starting point.
e. Kinetic energy is conserved because the speed of the system is zero before and after the
collision.
____ 51. The collision time between a bullet and a block of wood is best measured in
a. nanoseconds
d. seconds
b. microseconds
e. hours
c. milliseconds
____ 52. Without knowing any other information than is given in the diagram below, which deductions could be true?
a. The eastbound car was travelling faster.
b. The northbound car was lighter.
c. Both cars had the same speed.
d. two of A, B, and C
e. all of A, B, and C
Completion
Complete each sentence or statement.
53. Linear momentum depends on both the ____________________ and the velocity of an object.
54. A rotating object possesses ____________________ momentum.
55. The change in momentum of an object is called the ____________________.
56. The proper unit for momentum is ____________________ and the proper unit for impulse is
____________________.
57. If the net force acting on a system of interacting objects is zero, then linear momentum is
____________________.
58. Momentum is conserved in a system unless a(n) ____________________ net force acts on the system.
59. A ball is dropped and bounces back to its original height. The collision between the ball and the ground was
____________________.
60. A ball is dropped and bounces back to 90% of its original height. The collision between the ball and the ground
was ____________________.
61. If you squeeze a rubber ball and it springs back slowly, a collision involving that ball will most likely be
____________________.
62. If you squeeze a rubber ball and it springs back quickly, a collision involving that ball will most likely be
____________________.
Short Answer
63. Why is “follow-through” so important for maximizing speeds in sporting activities?
64. A 57-g tennis ball travelling at 28 m/s is hit straight back with the same velocity. Determine the average force
on the tennis ball if the racket is in contact with the ball for 4.9 ms.
65. A blazing spike of a 0.290-kg volleyball is blocked at the net. It is originally travelling at 18.3 m/s and bounces
straight back at 14.9 m/s after being in contact with the blockers arms for a total of 18.2 ms. What average force
did the blocker exert on the ball?
66. A raw egg dropped from a height of 1.0 m will break if it lands on a concrete floor, but not if it lands on a thin
sponge, even though it experiences the same impulse from each type of drop. Explain why.
67. Why is the “follow-through” of a badminton racket important?
68. Many vehicles produced today are designed with “crumple zones.” How does this feature protect the occupants
of the car?
69. If a person is standing in a stationary canoe, the total momentum of the person–canoe system is zero. If he walks
forward and then stops, both the canoe and person are moving.
(a) Is momentum conserved?
(b) What force is acting on the system?
70. Give two observations that would enable you to conclude that the bounce of a superball is not a completely
elastic collision.
71. The captain of a small barge notices the front corner of the boat is on a collision course with a edge of a small
pier. What could he ask the passengers to do to help him avoid a collision?
72. As a car coasts down a hill, it gains momentum. State the system that contains the car and where momentum is
conserved. Where does the momentum gained by the car come from?
73. During an elastic collision between a superball and the ground, the superball comes to rest for a brief instant.
Where is the energy stored?
74. Why are perfectly elastic collisions so unlikely?
75. A 0.25-kg snowball moving at 15 m/s [E] collides and sticks with a 1.9-kg toy truck travelling at 2.8 m/s [W].
Neglecting friction, calculate the velocity of the snowball–truck system after the collision.
76. A 25-kg bag of cement thrown at 2.5 m/s [E] is caught by a person sliding 1.8 m/s [E] on a frictionless surface.
If the velocity after the catch is 2.0 m/s, calculate the mass of the person.
77. Describe two features of a hockey helmet that help minimize head injury from a slapshot that hits the helmet.
78. A billiard ball collides with an identical stationary billiard ball causing the balls to travel out with speeds of 3.0
m/s and 4.0 m/s at 90º to each other as shown below. Calculate the initial speed of the moving billiard ball.
79. A common novelty sold at many stores consists of five steel balls suspended in a row as shown below. When
one is pulled back and released, what happens and why? The collisions between the balls are nearly elastic.
80. When you jump off a hay wagon perpendicular to the direction of motion, the hay wagon does not move off in
the opposite direction. Why not?
81. Why do you feel the “kick back” of a gun?
82. Many high-power hand guns need to be held with two hands. Why?
83. At a shooting range for hand guns, you often observe the shooters bend their elbows and allow the gun to move
up. Why?
84. How is an inelastic collision different than a completely inelastic collision?
85. Frictional forces are large for colliding vehicles during a car crash. Is conservation of momentum still useful in
analyzing these crashes?
86. An arrow undergoing projectile motion passes through an apple while travelling at 45º above the horizontal.
Can conservation of linear momentum be used to solve this problem?
87. What advice could be useful to a person who drives a car and habitually cuts in front of large trucks on the
highway? Use your knowledge or physics and collisions in your answer.
88. By observing the aerial diagram of an accident scene between two identical cars, which car was travelling more
quickly?
Problem
89. Two common and identical carts are used to perform an experiment. Cart A is pushed toward the stationary cart
B with a velocity of 2.6 m/s. After the collision, cart A bounces back with a speed of 0.8 m/s and cart B moves
of with a speed of 3.4 m/s. Why is this not possible?
90. Compare yourself sprinting at 7.0 m/s with a 63-g bullet travelling at 150 m/s.
(a) Which has a larger momentum?
(b) Which has more energy?
(c) Which is more dangerous? Why?
91. During a free dance program in figure skating, Victor (m = 71 kg) glides at 2.1 m/s to a stationary Shae-Lynn
(52 kg) and hangs on. How far will the pair slide after the “collision” if coefficient of kinetic friction µK between
their skates and the ice is 0.052?
92. A spring with a force constant of 89 N/m is compressed 8.7 cm and placed between two stationary dynamics
carts of mass 1.0 kg and 1.5 kg. If friction is negligible, determine the final speed of the more massive cart when
the spring is released.
93. A dog named Pinky throws a pan of lasagna (m = 2.3 kg) at his friend Flowers. The pan hits and sticks to
Flowers (m = 6.7 kg), who then slides a total of 2.2 m in 1.4 s. How fast was the lasagna moving before the
impact?
94. A 34-g bullet travelling at 120 m/s embeds itself in a wooden block on a smooth surface. The block then slides
toward a spring and collides with it. The block compresses the spring (k = 99 N/m) a maximum of 1.2 cm.
Calculate the mass of the block of wood.
95. A 0.40-kg cue ball makes a glancing blow to a stationary 0.30-kg billiard ball so that the cue ball deflects with a
speed of 1.2 m/s at an angle of 30.0º from its original path. Calculate the original speed of the cue ball if the
billiard ball ends up travelling at 1.5 m/s.
96. A small explosive charge is placed in a rubber block resting on a smooth surface. When the charge is detonated,
the block breaks into three pieces. A 200-g piece travels at 1.4 m/s, and a 300-g piece travels at 0.90 m/s. The
third piece flies off at a speed of 1.8 m/s. If the angle between the first two pieces is 80º, calculate the mass and
direction of the third piece. Assume two significant digits for each value.
97. During a game of billiards, the 0.30-kg cue ball, travelling at 2.1 m/s, glances off a stationary 0.28-kg billiard
ball so that the billiard ball moves off at 1.4 m/s at an angle of 38º from the cue ball’s original path. Find the new
speed of the cue ball.
98. A 63-kg student stands on a 34-kg cart that is free to move in any direction. The cart and student are moving
together with a velocity of 3.2 m/s [W]. The student then starts to walk so that her velocity is 1.8 m/s [25º W of
N] relative to the floor. Calculate the new velocity of the cart.
99. A 38-g bullet is fired with a speed of 180 m/s into a 5.0-kg sandbag pendulum that is free to swing. To what
maximum vertical height will the pendulum rise?
100. A bullet with a mass of 45 g is fired into a 8.3-kg block of wood resting on a floor against a spring. This ideal
spring (k = 76 N/m) has a maximum compression of 28 cm. What was the initial speed of the bullet?
101. A 1.8-kg block, initially at rest, slides down a frictionless ramp that is angled at 35º to the horizontal. At a point
0.45 m down the slope it collides with and sticks to a stationary block of mass 1.1 kg. The blocks then continue
another 0.88 m down the ramp. How long does the whole event take? (For those of you wondering how a block
is stationary on a frictionless ramp, it was projected up the ramp from below so it had no speed at the time of
impact.)
102. A 1.5-kg cart rolls along a horizontal table at a constant speed of 1.7 m/s. A ball of soft putty is dropped from a
stationary hand onto the cart as it passes underneath. If the speed of the cart is reduced to 0.73 m/s, calculate the
mass of the ball of putty.
103. Two carts of mass 12 kg and 15 kg move toward each other with speeds of 2.3 m/s and 1.5 m/s respectively. If
the collision between them is completely inelastic, calculate the velocity of the 15-kg cart after the collision.
Essay
104. Different types of rubber vary in elasticity from nearly elastic to almost completely inelastic. Write how an
application of each type has affected our society.
105. Mass, elasticity, momentum, and energy are very important concepts to consider in the design of a vehicle.
Provide support for four different ways designers might consider these concepts in their design.
106. Bowling, crokinole, and billiards are common forms of recreation that are based almost entirely on collisions.
Choose one activity and describe several ways in which it has affected your life.
107. Safety during sporting events becomes increasingly important as people and machines get faster and push the
limits of human accomplishment. Choose a sporting event and, referring to concepts covered in this unit,
explain how safety equipment minimizes risk of injury and how it has affected the sport.
Answer Section
MODIFIED TRUE/FALSE
1.
4.
7.
10.
13.
F, vector
T
T
F, is conserved
T
2.
5.
8.
11.
14.
T
F, speed direction and mass are
F, maintain its speed
T
F, can
3.
6.
9.
12.
15.
F, does not accurately represent
T
T
T
F, has reduced
17.
22.
27.
32.
37.
42.
47.
52.
C
E
A
A
D
B
D
E
18.
23.
28.
33.
38.
43.
48.
C
E
C
E
D
E
A
19.
24.
29.
34.
39.
44.
49.
E
C
B
C
E
B
A
20.
25.
30.
35.
40.
45.
50.
A
B
B
C
D
D
D
54.
59.
angular
elastic
55.
60.
impulse
inelastic
56.
61.
kg⋅m/s, N⋅s
inelastic
57.
62.
conserved
elastic
MULTIPLE CHOICE
16.
21.
26.
31.
36.
41.
46.
51.
E
D
D
D
B
D
E
C
`
COMPLETION
53. mass
58. external
SHORT ANSWER
63. By continuing the motion of the striking object, you increase the contact time and the impulse transferred to the
ball. This extra impulse translates into a faster speed.
64. The average force acting on the ball is 6.5 × 102 N.
65. The average force acting on the ball is 529 N.
66. The sponge slows the egg down more slowly than the concrete. Since the impulse is the same, the larger time
from the sponge means a much smaller force is exerted on the egg.
67. The follow-through allows the racket to be in contact with the shuttlecock for a longer period of time, imparting
a larger impulse and, therefore, a faster speed to the shuttlecock.
68. The crumple zone is designed to maximize the time (and the distance) over which the force to stop the car is
exerted. This reduces the size of the force that acts on the passengers, minimizing the injury.
69. (a)
Momentum is not conserved because the total momentum of the person–canoe system before and after
is not the same.
(b) The force that is acting on the system is fluid friction. (Other answers are bouyant force and gravitational
force.)
70. - The ball does not reach its original height after the bounce. (some loss of energy)
- Sound is produced. (sound energy must come from original kinetic energy)
71. By having the passengers walk to the same side of the boat as the pier, the boat will move away from it, helping
to avoid a collision.
72. The system is the Earth–car system. The Earth is moving toward the car to offset the momentum the gained by
the car. (The Earth would have negative momentum.)
73. The energy is stored as elastic potential energy in the deformed shape of the ball.
74. For an elastic collision to take place, all of the initial kinetic energy possessed by the objects must be transferred
to the objects after the collision with no loss. No loss of energy is difficult to achieve since some thermal energy
is always generated.
75. The final velocity is 0.73 m/s [W].
76. The mass of the person is 62 kg.
77. The snug fit transmits the force to the whole head instead of just one part. The cushioned padding increases the
time to stop and therefore reduces the force necessary to impart the impulse to the puck.
78. The initial speed of the billiard ball was 5.0 m/s.
79. When the ball strikes the first identical ball, all of the momentum will be transferred to it. This will continue
along the line until only the last ball swings up into the air.
80. The force of friction (an external force to the system) acts on the wagon.
81. The “kick back” is caused by the impulse the bullet imparts to the gun. The person shooting the gun acts as the
external force to stop this motion and can feel the gun accelerating toward him.
82. Since the bullet is fired at a very high speed, it has a large impulse applied to it. This is applied to the gun in the
opposite direction. After the bullet is ejected, the force that one hand is capable of applying is insufficient, so it
is suggested that two hands are used.
83. This allows the recoil distance to be larger since their arms can easily bend. Since the recoil takes more time, the
force is decreased. The shooters use this technique to minimize the force required to remove the impulse given
to the gun after the shot is fired.
84. The completely inelastic collision loses the maximum amount of kinetic energy (usually a hit and stick). An
inelastic collision may still be almost elastic (such as the bounce of a superball).
85. Yes. The forces of friction are large, but the crashes occur so quickly that the frictional forces do not play a
major role in the actual collision. They just slow vehicles down afterward.
86. Conservation of linear momentum can be used. The gravitational effects are insignificant during the brief
interaction between the apple and the arrow.
87. Several possible answers, but most importantly: During a collision, trucks have a much larger mass and are
much less likely to suffer large accelerations and the associated damage that you will.
88. The eastbound car had more momentum. Since the cars are identical, the eastbound car must have been moving
faster.
PROBLEM
89. There is more kinetic energy after the collision than before. This is not possible.
90. (a)The student has a much larger momentum.
(b)The student also has a larger kinetic energy.
(c) The bullet is more dangerous because all of the energy is concentrated on a small part of a target (i.e., a tree,
a target, or a person). The work done to stop it is only supplied by a small area, and it passes through many parts
before enough work can be done to stop it. The person has the work supplied by a larger surface area and is not
as dangerous.
91. The pair coast a total of 1.4 m after the collision.
92. The final speed of the more massive cart is 0.42 m/s.
93. The initial speed of the lasagna is 12 m/s.
94. The mass of the wooden block is 12 kg.
95. The initial speed of the cue ball was 2.0 m/s.
96. The mass of the third piece is 0.23 kg and is moving 141º from the 200-g piece (139º from the 300-g piece.)
97. The new speed of the cue ball is 1.3 m/s.
98. The new velocity of the cart is 8.3 m/s [21º S of W]
99. The sandbag will rise 9.4 cm vertically.
100. The impact speed of the bullet was 1.6 × 102 m/s.
101. The event takes 0.76 s.
102. The mass of the ball of putty is 2.0 kg.
103. The final speed of the 15-kg cart is 0.19 m/s.
ESSAY
104. Possible topics:
Elastic – “superballs” and applications for recreation, sports (lacrosse), childhood experiences. Affect on
society is a common (because it is inexpensive) childhood experience.
Inelastic – bumpers used in manufacturing to stop (without bouncing) boxes to alter direction of travel. To
minimize bounce from vehicle collisions. Effect on society is to minimize injury in collisions, and to increase
the efficiency of manufacturing to make our society more industrialized.
105. Possible ideas
- lower mass to reduce power needed to speed the vehicle up
- bumper design to minimize bounce
- crumple zones to minimize forces on passengers during rapid accelerations
- crumple zones to maximize energy absorption
- air bags to cushion passengers (impulse)
106. Possible considerations:
- personal memories associated with it
- learning experiences related to collisions that helped with a specific situation
- local establishments known for these forms of entertainment, or ways they think about people who go to them
107. Some possible sports
- racing (of anything such as cars, bobsleigh, skiing, boats)
- hockey or football
- high jump (and a number of other track events)
Some of the concepts
- impulse (increasing the time of acceleration to minimize force)
- momentum (strapping helmet to car seat because of added momentum the neck cannot withstand.)