7th Grade - CHpater 4 ONLINE REVEIW
Modified True/False
Indicate whether the statement is true or false. If false, change the identified word or phrase to make the statement true.
____ 1. To locate a mall close to you, you need to know it's distance. _________________________
____ 2. The speed you read on your speedometer is the constant speed. _________________________
____ 3. When you ride your bike around a corner at 10 m/s, you are accelerating. _________________________
____ 4. To determine if an object has changed position, you need to know it's position relative to another object. _________________________
____ 5. Acceleration is caused by any forces. _________________________
____ 6. An example of a contact force is magnetism. _________________________
____ 7. You push on a book and it moves. The forces acting on it must be action-reaction forces. _________________________
____ 8. If an unbalanced force is acting on a rope, the rope will accelerate in the direction of the unbalanced force. _________________________
____ 9. If an astronaut were to land on Jupiter, his mass would increase. _________________________
____ 10. An insect falls from a twenty-story building and walks away when he hits the sidewalk because of contact forces. _________________________
____ 11. Sliding friction keeps you in the seat when a car goes around a corner. _________________________
____ 12. Forces always occur alone. _________________________
____ 13. If you throw a ball into the air, Earth exerts a force on the ball. The ball in the air exerts no force. _________________________
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____ 14. Electric, magnetic, and gravitational forces are all examples of which type of force?
a.
balanced
b.
contact
c.
non-contact
d.
unbalanced
____ 15. Which of the following has a net force of zero?
a.
balanced force
b.
buoyant force
c.
gravitational force
d.
unbalanced force
____ 16. Max is pushing a book across a table. When he stops pushing, the book slows down and stops. This is an example of which force?
a.
air resistance
b.
buoyancy
c.
gravity
d.
sliding friction
____ 17. When does a gravitational force between two objects increase?
a.
when the mass of the objects increases
b.
when the speed of the objects increases
c.
when the mass of the objects decreases
d.
when the speed of the objects decreases
____ 18. An object at rest remains at rest. An object in motion keeps moving in a straight line at a constant speed. Which of Newton’s laws of motion does this describe?
a.
first law
b.
second law
c.
third law
d.
first and third laws together
____ 19. Mark is traveling 3 mi north at 2 mph. Which of the following can be figured out with this information?
a.
acceleration
b.
average speed
c.
displacement
d.
velocity
____ 20. Susan made a diagram to show how the relationship between a buoyant force and gravity.
Which answer BEST describes the relationship shown in the diagram?
a.
Buoyancy and gravity together balance an object.
b.
Buoyant forces move at a faster rate than gravity.
c.
Gravity is more powerful than buoyancy.
d.
Objects do not know whether they will be pulled up or down
____ 21. Which law of motion says that the ground pushes back on you when you push down on it?
a.
first law
b.
second law
c.
third law
d.
fourth law
____ 22. The Average Speed equation states that average speed in meters per second equals distance in meters divided by time in seconds. If Jan travels 63 m in 7 s, what is her average speed?
a.
7 m/s
b.
9 m/s
c.
14 m/s
d.
63 m/s
____ 23. When is an object NOT accelerating?
a.
when it changes speed
b.
when it changes direction
c.
when it changes force
d.
when it changes velocity
____ 24. Donna measured the displacement and time for a traveling object.
What is the velocity of the object?
a.
2 km/h south
b.
3 km/h south
c.
4 km/h south
d.
6 km/h south
____ 25. According to Newton’s second law of motion, how is acceleration related to net force?
a.
When net force on an object increases, acceleration increases.
b.
When net force on an object decreases, acceleration increases.
c.
When acceleration changes, net force stays the same.
d.
When net force changes, acceleration stays the same.
____ 26. Which statement best describes Newton’s third law of motion?
a.
All forces are equal.
b.
An object at rest tends to stay at rest.
c.
Forces always act in pairs.
d.
Some forces have no reaction.
____ 27. Motion is change in ____.
a.
speed
c.
force
b.
velocity
d.
position
____ 28. ____ is rate of change of position.
a.
Speed
c.
Acceleration
b.
Velocity
d.
Displacement
____ 29. You travel 200 km in 2 h. Your ____ speed is 100 km/h.
a.
constant
c.
instantaneous
b.
average
d.
initial
____ 30. When a car slows down at a traffic light, it is ____.
a.
accelerating
c.
decreasing its displacement
b.
traveling at constant velocity
d.
changing direction
____ 31. You hear that a storm is moving 15 km/h north. You have been given the storm's ____.
a.
constant speed
c.
velocity
b.
acceleration
d.
average speed
____ 32. Inertia is a measure of the ____ of an object.
a.
weight
c.
constant speed
b.
mass
d.
acceleration
____ 33. The unit of force is ____.
a.
m/s
c.
the joule
b.
the hertz
d.
the newton
____ 34. When two birds are pulling on a worm and the worm moves toward the first bird, you know that the forces are ____.
a.
long-range
c.
unbalanced
b.
action-reaction
d.
balanced
____ 35. An unbalanced force acting on an object causes it to ____.
a.
move at constant speed
c.
not change its velocity
b.
continue in a straight line
d.
accelerate
____ 36. A planet is discovered that is the same size as Earth and has the same gravitational acceleration, but has twice the mass. If you weigh 700 N on Earth, on the new planet you would weigh ____.
a.
350 N
c.
1,400 N
b.
700 N
d.
2,800 N
____ 37. The force that opposes motion is ____.
a.
a balanced force
c.
an accelerating force
b.
an unbalanced force
d.
friction
____ 38. Every force has a(n) ____ force.
a.
reaction
c.
opposite
b.
long-range
d.
accelerating
____ 39. You throw a ball into the air. As the ball leaves your hand, the force(s) acting on it is/are ____.
a.
gravity
c.
balanced
b.
your hand
d.
gravity and your hand
Completion
Complete each statement.
40. If you walk one mile to a store and one mile back, your distance is ____________________ and your displacement is ____________________.
41. If you ride your bike 2 miles on a straight road between Gooseberry Junction and Happy Valley, your distance is ____________________ and your displacement is ____________________.
42. ____________________ is the change in velocity divided by the change in time.
43. Speeding up, slowing down, and going around curves are examples of ____________________.
44. If you are riding on a skateboard and it stops suddenly, your body keeps moving forward. This is because of ____________________.
45. A(n) ____________________ is a push or a pull.
46. Forces that change an object's motion by touching the object are ____________________ forces.
47. A spacecraft orbits the Earth at a constant speed. The forces acting on it must be ____________________.
48. Acceleration due to gravity at the Earth's surface is ____________________.
49. A car going around a corner, hits an icy path, and skids off the road. This represents a change from rolling friction to ____________________ friction.
50. Wagons have wheels instead of runners because ____________________ friction is less than ____________________ friction.
51. When you catch a ball, the ball creates force on your hand. The reaction force is ____________________.
52. If you throw a ball into the air, at the top of the path the force(s) acting on the ball is/are ____________________.
Choose the term or phrase that best completes each sentence.
53. If you drive from New York to San Francisco by way of Mt. Rushmore, Yellowstone National Park, and Branson, Missouri, your distance traveled is ____________________ (greater than, less than, the same as) your displacement.
54. When your feet push on the floor so that you can walk across the room, you move but the floor doesn’t. The force of the floor on your feet is ____________________ (greater than, less than, the same as) the force of your feet on the floor.
55. Standing still in a windstorm is an example of ____________________ (static, sliding, rolling) friction between your feet and the ground.
56. To push a box across the floor takes more force than to push the same box on wheels across the floor. This shows that rolling friction is ____________________ (greater than, less than, equal to) sliding friction.
57. In order to keep a race car going around a circular track at constant speed, ____________________ (no force, a balanced force, an unbalanced force) is needed.
58. A reaction force is created ____________________ (before, after, at the same time as) its action force.
59. The force needed to accelerate a full-size car to a given velocity is ____________________ (greater than, less than, equal to) the force needed to accelerate a motorcycle to the same velocity.
60. The displacement of a car driving a winding road up a mountain is ____________________ (greater than, less than, the same as) the distance the car travels.
61. When you push off of the side of a swimming pool, the force of your foot on the wall is created ____________________ (before, after, at the same time as) the force of the wall on your foot.
62. When a ball starts to fall through the air, the force of air resistance on the ball is ____________________ (greater than, less than, the same as) the force of gravity.
63. The mass of an astronaut ____________________ (increases, decreases, remains the same) when the astronaut goes on a space walk.
64. A crumpled piece of paper falls to the ground faster than a smooth piece because of ____________________.
65. When you push a book across your desk, the force of your hand is ____________________ the force of static friction.
66. The force needed to accelerate a bowling ball to a given velocity is ____________________ the force needed to accelerate a soccer ball to the same velocity.
67. A radio-controlled plane flies 75 m north, then 95 m south. Its ____________________ is 20 m south.
68. A car that travels 200 km in 2 h has a(n) ____________________ speed of 100 km/h.
69. ____________________ keeps you from sliding backward when you climb a hill.
70. ____________________ is the tendency of a body to resist change in its motion.
71. Forces always occur in equal but opposite ____________________.
Matching
Match each item with the correct description below.
a.
static friction
k.
Unbalanced forces
b.
force
l.
Acceleration
c.
rolling friction
m.
Inertia
d.
displacement
n.
Speed
e.
first law of motion
o.
Second law of motion
f.
Newton’s laws of motion
p.
Friction
g.
Sliding friction
q.
Air resistance
h.
Velocity
r.
Mass
i.
Balanced forces
s.
Newton (N)
j.
Third law of motion
t.
weight
____ 72. the distance and direction between starting and ending positions
____ 73. the distance traveled divided by the time needed to travel the distance
____ 74. change in velocity divided by the amount of time required for the change to occur
____ 75. displacement divided by time
____ 76. an object will remain at rest or move in a straight line with constant speed unless it is acted upon by a force
____ 77. equal forces that move in opposite directions
____ 78. a push or a pull
____ 79. forces that move in opposite directions that are not of equal strength
____ 80. a force that resists motion
____ 81. an object acted upon by an unbalanced force will accelerate in the direction of the force
____ 82. forces always act in equal but opposite pairs
____ 83. Air molecules act on the forward-moving surface of an object, slowing its motion.
____ 84. The type of friction that makes a tire turn and a ball roll is called ____.
____ 85. the friction that occurs when two surfaces slide past each other
____ 86. the friction that hinders a stationary object from moving on a surface when a force is applied to that object
____ 87. a force that can change when acceleration due to gravity changes
____ 88. a measure of the amount of matter in an object
____ 89. measures an object’s tendency to remain at rest or keep moving with constant velocity
____ 90. used to measure force
____ 91. a set of rules used to predict and explain motion
Match Newton’s laws of motion with the examples given.
a.
Newton’s first law
c.
Newton’s third law
b.
Newton’s second law
____ 92. A magician pulls the table cloth off a table, leaving the dishes on the table.
____ 93. A ball rolling across the floor eventually comes to a stop.
____ 94. A rower’s arms push the oars against the water. The boat moves forward after the water pushes against the oars.
____ 95. A rock moves slower when shot out of a slingshot than a pebble shot out of the same slingshot.
____ 96. You jump off a raft in the swimming pool, and when you turn around to get back on the raft, the raft has floated off in the opposite direction.
Match the unit with the quantity it measures.
a.
second
d.
m/s2
b.
newton
e.
meter
c.
m/s
____ 97. speed
____ 98. distance
____ 99. force
____ 100. time
____ 101. acceleration
Short Answer
102.
Explain the difference between speed and velocity.
103.
Mr. French’s class is using a toy car to study Newton’s laws of motion.
Part A What does Newton’s first law state?
Part B Give an example of how the class can use the toy car to demonstrate how the law works.
104.
Compare and contrast distance and displacement.
105.
Compare and contrast speed and velocity.
106.
If you run three laps around a circular race track at 5 m/s, what do you know about your speed, velocity, and acceleration?
107.
Is it necessary for an object to be in motion if it has forces acting on it? Why or why not?
108.
"If no forces are acting on a moving object, it will eventually come to rest." Comment on this statement.
109.
If you were playing football on the space station, would it be as hard to stop a 150-kg lineman as it would be on Earth? Why or why not?
110.
How is force similar to displacement and velocity?
111.
You drop a pebble from a bridge and it goes faster and faster before it hits the water. What do you know about the forces acting on the pebble?
112.
If a body is in motion at constant speed in a straight line, what, if any, forces could be acting on it?
113.
How could you decrease the force a horse needed to pull a wagonload of hay?
114.
For a long time, all experiments showed that a force had to be applied to keep a body in motion at constant velocity. How does our knowledge of the force of friction help us to understand, now, that this isn't true?
Figure 23-1
115.
In Figure 23-1, identify two pairs of action-reaction forces involving the rope.
116.
In Figure 23-1, identify two balanced forces involving the rope.
117.
In Figure 23-1, if the black dog starts pulling on the rope harder than the white dog, what will happen to the rope?
118.
In Figure 23-1, how could the rope-on-black-dog force be increased?
119.
In Figure 23-1, if the rope moves toward the white dog, what do you know about the forces on the rope?
120.
If you throw a ball into the air, after it leaves your hand, what is/are the net force(s) acting on it? Describe the ball's acceleration.
121. A high speed train travels south for 2.00 h for a distance of 454 km. What is its average velocity?
122. A coasting car slows down from 27 m/s to 24 m/s in 6 s. What is the car’s acceleration?
123. Calculate the force necessary to accelerate a 0.14-kg hardball at a rate of 100 m/s2.
124. A car travels 528 km in six hours. Find its average speed.
125. The maximum acceleration of a fist in a karate punch is 3800 m/s2. The mass of the fist is 0.70 kg. If the fist hits a wooden block, what force does the wood place on the fist?
126. When a ball is dropped it is easy to see that Earth exerts a force on it. Why can’t you tell that the ball exerts a force on Earth?
127. If you and your friend ride bumper cars at the fair, what happens, in terms of Newton’s third law, when they collide?
128. If you bump into a heavy desk sitting on a carpet, it doesn’t move. Explain.
129. Is it possible to have a single force? Explain why or why not.
130. It has been found that when a karate blow of a fist strikes a wooden block, the block can exert a force of 2,450 N on the hand. What force must be put on the block to break it?
Problem
131.
0.30 s after seeing a puff of smoke rise from the starter's pistol, the sound of the firing of the pistol is heard by the track timer 100 m away. What is the speed of sound?
132.
A top-fuel dragster accelerates from rest to a velocity of 100 m/s in 8 s. What is the acceleration?
133.
On Planet Zorg, a 30-kg barbell can be lifted by only exerting a force of 180 N. What is the acceleration of gravity on Planet Zorg?
134.
A racing car has a mass of 750 kg. It undergoes an acceleration of 4.00 m/s2. What is the net force acting on the car?
Essay
135. An astronaut in the space shuttle turns a screwdriver clockwise. The astronaut starts to rotate in a counterclockwise direction. Why does this happen?
136. You are worried about a severe storm in your area. You hear a weather broadcast that says that the storm is moving at a speed of 25 km/h. Is this all you need to know for safety? Explain why or why not in terms of speed and velocity.
137. You ride three full turns around on a merry-go-round horse. What is your displacement? Your speed is constant; is your velocity constant? Why or why not?
138. A dog on a chain is fastened to the side of a house.
a. As the dog pulls on the end of the chain, name two pairs of action-reaction forces acting on the chain.
b. What are the balanced forces on the chain?
c. What happens to the forces on the chain if the dog pulls the chain away from the wall and runs to play?
7th Grade - CHpater 4 ONLINE REVEIW
Answer Section
MODIFIED TRUE/FALSE
1. ANS: F, displacement
PTS: 1 DIF: Webb's I OBJ: 1/1 STA: SC.C.1.3.1
2. ANS: F, instantaneous
PTS: 1 DIF: Webb's I OBJ: 2/1 STA: SC.C.1.3.1
3. ANS: T PTS: 1 DIF: Webb's I
OBJ: 2/1 STA: SC.C.1.3.1
4. ANS: T PTS: 1 DIF: Webb's I
OBJ: 1/1 STA: SC.C.1.3.1
5. ANS: F, unbalanced
PTS: 1 DIF: Webb's I OBJ: 6/2 STA: SC.C.1.3.1
6. ANS: F, long-range
PTS: 1 DIF: Webb's I OBJ: 4/2 STA: SC.C.2.3.1 SC.C.2.3.2
7. ANS: F, unbalanced
PTS: 1 DIF: Webb's I OBJ: 6/2 STA: SC.C.2.3.2 SC.C.2.3.6
8. ANS: T PTS: 1 DIF: Webb's I
OBJ: 6/2 STA: SC.C.2.3.6
9. ANS: F, remain the same
PTS: 1 DIF: Webb's I OBJ: 7/3
10. ANS: F, air resistance
PTS: 1 DIF: Webb's I OBJ: 8/3 STA: SC.C.2.3.2
11. ANS: F, Static
PTS: 1 DIF: Webb's I OBJ: 8/3 STA: SC.C.2.3.2
12. ANS: F, in pairs
PTS: 1 DIF: Webb's I OBJ: 10/4 STA: SC.C.2.3.2 SC.C.2.3.6
13. ANS: F, a force on Earth
PTS: 1 DIF: Webb's I OBJ: 11/4 STA: SC.C.2.3.1
MULTIPLE CHOICE
14. ANS: C PTS: 1 DIF: Webb's I STA: SC.C.2.3.1
15. ANS: A PTS: 1 DIF: Webb's I STA: SC.C.2.3.3
16. ANS: D PTS: 1 DIF: Webb's II STA: SC.C.2.3.2 SC.C.2.3.3
17. ANS: A PTS: 1 DIF: Webb's II STA: SC.C.2.3.7
18. ANS: A PTS: 1 DIF: Webb's I STA: SC.C.2.3.5
19. ANS: D PTS: 1 DIF: Webb's I STA: SC.C.1.3.1
20. ANS: C PTS: 1 DIF: Webb's II STA: SC.C.2.3.1
21. ANS: C PTS: 1 DIF: Webb's II STA: SC.C.2.3.3
22. ANS: B PTS: 1 DIF: Webb's II STA: SC.C.1.3.1
23. ANS: C PTS: 1 DIF: Webb's I STA: SC.C.1.3.1
24. ANS: B PTS: 1 DIF: Webb's II STA: SC.C.1.3.1
25. ANS: A PTS: 1 DIF: Webb's II STA: SC.C.2.3.6
26. ANS: C PTS: 1 DIF: Webb's II STA: SC.C.2.3.3
27. ANS: D PTS: 1 DIF: Webb's I OBJ: 1/1
STA: SC.C.1.3.1
28. ANS: A PTS: 1 DIF: Webb's I OBJ: 2/1
STA: SC.C.1.3.1
29. ANS: B PTS: 1 DIF: Webb's I OBJ: 3/1
STA: SC.C.1.3.1
30. ANS: A PTS: 1 DIF: Webb's I OBJ: 2/1
STA: SC.C.1.3.1 SC.C.2.3.3 SC.C.2.3.5
31. ANS: C PTS: 1 DIF: Webb's I OBJ: 2/1
STA: SC.C.1.3.1
32. ANS: B PTS: 1 DIF: Webb's I OBJ: 5/2
33. ANS: D PTS: 1 DIF: Webb's I OBJ: 4/2
34. ANS: C PTS: 1 DIF: Webb's I OBJ: 6/2
STA: SC.C.2.3.2
35. ANS: D PTS: 1 DIF: Webb's I OBJ: 10/4
STA: SC.C.2.3.2
36. ANS: C PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.A.1.3.2 SC.C.2.3.1
37. ANS: D PTS: 1 DIF: Webb's I OBJ: 8/3
STA: SC.C.2.3.2 SC.C.2.3.5
38. ANS: C PTS: 1 DIF: Webb's I OBJ: 10/4
STA: SC.C.2.3.3
39. ANS: D PTS: 1 DIF: Webb's I OBJ: 10/4
STA: SC.C.2.3.1
COMPLETION
40. ANS: 2 miles, 0
PTS: 1 DIF: Webb's II OBJ: 1/1 STA: SC.C.1.3.1
41. ANS: 2 miles, 2 miles
PTS: 1 DIF: Webb's II OBJ: 1/1 STA: SC.C.1.3.1
42. ANS: Acceleration
PTS: 1 DIF: Webb's I OBJ: 2/1 STA: SC.C.1.3.1
43. ANS: acceleration
PTS: 1 DIF: Webb's I OBJ: 2/1 STA: SC.C.1.3.1
44. ANS: inertia
PTS: 1 DIF: Webb's I OBJ: 5/2 STA: SC.C.2.3.6
45. ANS: force
PTS: 1 DIF: Webb's I OBJ: 4/2 STA: SC.C.2.3.1 SC.C.2.3.2
46. ANS: contact
PTS: 1 DIF: Webb's I OBJ: 4/2 STA: SC.C.2.3.2
47. ANS: balanced
PTS: 1 DIF: Webb's I OBJ: 6/2 STA: SC.C.2.3.1 SC.C.2.3.6
48. ANS: 9.8m/sec2
PTS: 1 DIF: Webb's I OBJ: 7/3 STA: SC.C.2.3.1
49. ANS: sliding
PTS: 1 DIF: Webb's I OBJ: 8/3 STA: SC.C.2.3.5
50. ANS: rolling, sliding
PTS: 1 DIF: Webb's II OBJ: 8/3 STA: SC.C.2.3.2
51. ANS: hand-on-ball
PTS: 1 DIF: Webb's II OBJ: 10/4 STA: SC.C.2.3.2
52. ANS: gravity, air resistance
PTS: 1 DIF: Webb's II OBJ: 10/4 STA: SC.C.2.3.2 SC.C.2.3.3
53. ANS: greater than
PTS: 1
54. ANS: the same as
PTS: 1
55. ANS: static
PTS: 1
56. ANS: less than
PTS: 1
57. ANS: an unbalanced force
PTS: 1
58. ANS: at the same time as
PTS: 1
59. ANS: greater than
PTS: 1
60. ANS: less than
PTS: 1
61. ANS: at the same time as
PTS: 1
62. ANS: less than
PTS: 1
63. ANS: remains the same
PTS: 1
64. ANS: air resistance
PTS: 1
65. ANS: greater than
PTS: 1
66. ANS: less than
PTS: 1
67. ANS: displacement
PTS: 1
68. ANS: average
PTS: 1
69. ANS: friction
PTS: 1
70. ANS: inertia
PTS: 1
71. ANS: pairs
PTS: 1
MATCHING
72. ANS: D PTS: 1
73. ANS: N PTS: 1
74. ANS: L PTS: 1
75. ANS: H PTS: 1
76. ANS: E PTS: 1
77. ANS: I PTS: 1
78. ANS: B PTS: 1
79. ANS: K PTS: 1
80. ANS: P PTS: 1
81. ANS: O PTS: 1
82. ANS: J PTS: 1
83. ANS: Q PTS: 1
84. ANS: C PTS: 1
85. ANS: G PTS: 1
86. ANS: A PTS: 1
87. ANS: T PTS: 1
88. ANS: R PTS: 1
89. ANS: M PTS: 1
90. ANS: S PTS: 1
91. ANS: F PTS: 1
92. ANS: A PTS: 1
93. ANS: A PTS: 1
94. ANS: C PTS: 1
95. ANS: B PTS: 1
96. ANS: C PTS: 1
97. ANS: C PTS: 1
98. ANS: E PTS: 1
99. ANS: B PTS: 1
100. ANS: A PTS: 1
101. ANS: D PTS: 1
SHORT ANSWER
102. ANS:
Speed is defined as the distance traveled divided by the time needed to travel that distance. It is a change in position over time. Velocity takes direction into account as well as distance and time. Velocity is the distance traveled in a certain direction divided by the time it takes to travel that distance.
PTS: 1 DIF: Webb's II STA: SC.C.1.3.1
103. ANS:
Part A Newton’s first law of motion states that forces acting on an object are balanced. An object at rest tends to stay at rest and an object in motion keeps moving in a straight line with a constant speed. The net force on the object remains the same.
Part B The class can demonstrate the law by observing the car at rest and then applying a force to make the car move. However, the net force on the object will change directions because of friction acting on the car. The car will eventually slow down and stop.
PTS: 1 DIF: Webb's III STA: SC.C.2.3.5
104. ANS:
They both involve a distance, but displacement also involves a direction.
PTS: 1 DIF: Webb's II OBJ: 1/1 STA: SC.C.1.3.1
105. ANS:
Both quantities measure speed, but velocity includes direction by calculating displacement.
PTS: 1 DIF: Webb's II OBJ: 2/1 STA: SC.C.1.3.1
106. ANS:
Your speed is constant. Your velocity is changing because you are changing direction. And, you are constantly accelerating because your velocity is changing.
PTS: 1 DIF: Webb's II OBJ: 2/1 STA: SC.C.1.3.1
107. ANS:
No, it is not necessary. The forces can be balanced and acting on an object that is at rest.
PTS: 1 DIF: Webb's II OBJ: 6/2 STA: SC.C.1.3.1 SC.C.2.3.3
108. ANS:
It is not true. If no forces act on a moving object, it will continue at constant velocity. It takes an unbalanced force to stop an object in motion.
PTS: 1 DIF: Webb's II OBJ: 5/2 STA: SC.C.2.3.5
109. ANS:
It would be just as hard because mass, and therefore inertia, does not change.
PTS: 1 DIF: Webb's II OBJ: 5/2 STA: SC.C.2.3.1 SC.C.2.3.2
110. ANS:
They all require a number (amount) and a direction.
PTS: 1 DIF: Webb's II OBJ: 6/2
111. ANS:
They are unbalanced. There is an unbalanced force causing acceleration.
PTS: 1 DIF: Webb's II OBJ: 6/2 STA: SC.C.1.3.1 SC.C.2.3.3
112. ANS:
There could be balanced forces acting on it.
PTS: 1 DIF: Webb's II OBJ: 6/2 STA: SC.C.1.3.1 SC.C.2.3.3 SC.C.2.3.5
113. ANS:
Possible answers: remove some of the hay from the wagon, reduce the rolling friction of the wheels.
PTS: 1 DIF: Webb's II OBJ: 10/4 STA: SC.C.2.3.3 SC.C.2.3.2
114. ANS:
The force of friction acts in opposition to motion. Therefore it is the force of friction which must be balanced in order to keep an object in motion in a constant velocity. Without friction, an object in motion at constant velocity would remain so unless acted upon by an unbalanced force.
PTS: 1 DIF: Webb's II OBJ: 10/4 STA: SC.C.2.3.5 SC.H.1.3.1
115. ANS:
black dog on rope; rope on black dog; white dog on rope; rope on white dog
PTS: 1 DIF: Webb's II OBJ: 10/4 STA: SC.C.2.3.2 SC.C.2.3.3
116. ANS:
white dog on rope; black dog on rope
PTS: 1 DIF: Webb's II OBJ: 9/3 STA: SC.C.2.3.3
117. ANS:
The rope will move in the direction of the black dog.
PTS: 1 DIF: Webb's II OBJ: 6/2 STA: SC.C.2.3.3
118. ANS:
If the black dog pulled harder on the rope.
PTS: 1 DIF: Webb's II OBJ: 6/2 STA: SC.C.2.3.3
119. ANS:
The forces on the rope are unbalanced. The white-dog-on-rope force is greater than the black-dog-on-rope force.
PTS: 1 DIF: Webb's II OBJ: 6/2 STA: SC.C.2.3.3
120. ANS:
The forces acting on the ball are hand-on-ball, gravity, and air resistance. After it leaves your hand, first it accelerates upward, then slows down, stops, and starts speeding up downward.
PTS: 1 DIF: Webb's II OBJ: 10/4 STA: SC.C.2.3.6
121. ANS:
v = d/t = 454 km/2.00 h = 227 km/h south
PTS: 1
122. ANS:
a = vf – vit = (24 m/s – 27 m/s)/6 s = –0.5 m/s2
PTS: 1
123. ANS:
F = ma = 0.14 kg ´ 100 m/s2 = 14 N
PTS: 1
124. ANS:
v = d/t = 528/6 h = 88 km/h
PTS: 1
125. ANS:
F = ma = 0.70 kg ´ 3,500 m/s2 = 2,450 N
PTS: 1
126. ANS:
Earth is so massive that the ball doesn’t accelerate it noticeably.
PTS: 1
127. ANS:
When the cars collide, each car exerts a equal but opposite force on the other car. The cars move apart in opposite directions.
PTS: 1
128. ANS:
Static friction between the desk and the carpet keeps the desk from moving.
PTS: 1
129. ANS:
It is not possible. For every action force there is a reaction force.
PTS: 1
130. ANS:
anything over 2,450 N
PTS: 1
PROBLEM
131. ANS:
s = d/t = 100 m/0.30s = 333 m/s
PTS: 1 DIF: Webb's II OBJ: 3/1 STA: SC.C.1.3.1 SC.C.1.3.2
132. ANS:
a = (vf – vl)/t = (100m/s – 0)/8 s = 12.5 m/s2
PTS: 1 DIF: Webb's II OBJ: 3/1 STA: SC.C.1.3.1
133. ANS:
a = F/m = 189 N/30 kg = 6.0 m/s2
PTS: 1 DIF: Webb's II OBJ: 7/3 STA: SC.C.2.3.7
134. ANS:
F = ma = 750 kg (4.00 m/s2) = 3,000 N
PTS: 1 DIF: Webb's II OBJ: 7/3 STA: SC.C.2.3.6
ESSAY
135. ANS:
When the astronaut exerts a clockwise force on the screwdriver, the screwdriver exerts an equal counterclockwise force on her.
PTS: 1
136. ANS:
You need to know more than just the speed. You need to know the direction the storm is traveling. You need to know not just the speed but the velocity.
PTS: 1
137. ANS:
Your displacement is zero because you are going around in a circle and end up where you started. Your velocity is not constant. You are constantly accelerating because you are constantly changing directions.
PTS: 1
138. ANS:
a. The action-reaction pairs are chain-on-wall and wall-on-chain and dog-on-chain and chain-on-dog.
b. dog-on-chain and wall-on-chain
c. The dog-on-chain force becomes greater than the wall-on-chain force and the chain moves toward the dog.
PTS: 1
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