7th Grade - CHpater 5 ONLINE REVIEW
True/False
Indicate whether the statement is true or false.
____ 1. When you perform work on an object you increase the energy of the object.
____ 2. A force at any angle to the direction of motion can perform work.
____ 3. Work is measured in joules.
____ 4. All forms of energy can do work.
____ 5. Under certain conditions, it is possible to get more work out of a machine than you put into it.
____ 6. Power is the rate at which a force is applied.
____ 7. The unit of power is the watt.
____ 8. Machines may allow you to do less work over a longer distance.
____ 9. The thread around a screw is a lever.
____ 10. The mechanical advantage of a wheel and axle is the radius of the wheel divided by the radius of the axle.
____ 11. A broom is an example of a wedge.
____ 12. Power and work are interchangeable terms.
____ 13. If you use a ramp that is 6 m long to move an object upward 1 m, then the mechanical advantage of the ramp is 6.
____ 14. You are doing NO work when you hold your 23-kg dog in your arms.
____ 15. You do 1 J of work if you use a force of 1 N for a distance of 1 m.
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____ 16. Which is NOT an example of a compound machine?
a.
bicycle
b.
can opener
c.
pulley
d.
scissor
____ 17. Jacob is pushing a shopping cart down a supermarket aisle. He is exerting forces in different directions on the shopping cart handle. Which force is doing the work?
a.
downward force
b.
forward force
c.
right angle force
d.
upward force
____ 18. Which response best describes power?
a.
The distance an object is moved.
b.
The force exerted on an object.
c.
The motion of an object.
d.
The rate at which work is done.
____ 19. In which way can a machine NOT make work easier?
a.
changing the amount of force needed
b.
changing the distance over which force is exerted
c.
changing the direction in which force is exerted
d.
changing the work by creating a new force
____ 20. Joey used a knife to cut a piece of bread. What is the work he applied to the knife called?
a.
friction
b.
input force
c.
mechanical advantage
d.
output force
____ 21. Hu made a chart to show the efficiency of three different machines.
Which machine has the highest ratio of output work to input work?
a.
Machine 1
b.
Machine 2
c.
Machine 3
d.
cannot tell
____ 22. Which is an example of a wheel and axle?
a.
baseball bat
b.
doorknob
c.
pulley
d.
screw
____ 23. How are an inclined plane and a wedge alike?
a.
Both have a flat, sloped surface.
b.
Both are compound machines.
c.
Both have the same mechanical advantage.
d.
Both have the same output force.
____ 24. Darren draws a diagram to show the forces exerted on an object. The arrows represent equal forces on the object.
How will the object be affected by the two equal forces?
a.
It will break.
b.
It will change direction.
c.
It will not be affected.
d.
It will not move.
____ 25. Which word best describes the ratio of an output force to an input force?
a.
distance
b.
efficiency
c.
friction
d.
mechanical advantage
____ 26. How does friction affect a machine’s efficiency?
a.
It increases it.
b.
It decreases it.
c.
It keeps it consistent.
d.
It does not affect it.
____ 27. The work equation states that work in joules equals force in newtons times distance in meters. If Sarah carries a box that weighs 35 N a distance of 3 m, how much work did she do?
a.
38 J
b.
70 J
c.
105 J
d.
175 J
____ 28. Tammy is standing still while holding a ten-pound bowling ball. Is she doing work?
a.
Yes, the ball is heavy.
b.
Yes, she is exerting a force on the object.
c.
No, she is not making the object move.
d.
No, she is exerting a force on the ground.
____ 29. Which one of the following is NOT an example of work being done?
a.
the Moon orbiting Earth
b.
pushing a box from the bottom of a hill to the top of the hill
c.
pulling a sled across a field covered with snow
d.
lifting a bookbag off the floor
____ 30. A fixed, single pulley that is used to lift a block does which one of the following?
a.
doubles the force required to lift the block
b.
decreases the force required to lift the block
c.
makes the block easier to lift by changing the direction of the force needed to lift it
d.
decreases the force required and changes the direction of the force required
____ 31. A slanted surface used to raise an object is a(n)____.
a.
efficiency board
c.
inclined plane
b.
effort ramp
d.
wedge
____ 32. A device that does work with only one movement and changes the size or direction of a force is a(n) ____.
a.
compound machine
c.
screw
b.
effort machine
d.
simple machine
____ 33. A bar that is free to pivot about a fixed point is a ____.
a.
fulcrum
c.
ramp
b.
lever
d.
wedge
____ 34. The rate at which work is done is called ____.
a.
efficiency
c.
force
b.
effort time
d.
power
____ 35. The work output of a machine divided by the work input is the ____ of the machine.
a.
efficiency
c.
power
b.
effort
d.
resistance
____ 36. The amount by which a machine multiplies an input force is called the ____.
a.
efficiency factor
c.
mechanical advantage
b.
fulcrum
d.
resistance force
____ 37. An inclined plane with one or two sloping sides forms a machine called a ____.
a.
pulley
c.
ramp
b.
lever
d.
wedge
____ 38. An inclined plane wrapped around a cylinder post is a ____.
a.
lever
c.
screw
b.
ramp
d.
wedge
____ 39. A machine that changes only the direction of a force has a mechanical advantage of ____.
a.
1
c.
10
b.
2
d.
100
____ 40. A winding mountain road is an example of a(n) ____.
a.
lever
c.
wedge
b.
inclined plane
d.
wheel and axle
____ 41. When two or more simple machines work together, they are called a(n) ____.
a.
compound machine
c.
screw
b.
effort machine
d.
simple machine
____ 42. A lever with a mechanical advantage greater than 1 is used to ____.
a.
change direction
c.
increase force
b.
increase distance
d.
decrease force
____ 43. Three of the following simple machines are basically the same. The one that does NOT belong with the group is the ____.
a.
lever
c.
wedge
b.
pulley
d.
wheel and axle
____ 44. An object is moving due east. You push the object. Work is being done at all times when you push ____.
a.
due west
c.
straight down
b.
due east
d.
at a 45° angle
____ 45. A ____ is an example of a compound machine.
a.
lawnmower
c.
baseball bat
b.
shovel
d.
wheel and axle
____ 46. The mechanical advantage tells you the number of times a machine increases the ____.
a.
net force
c.
output force
b.
stable force
d.
input force
____ 47. Work is equal to force times ____.
a.
power
c.
joules
b.
distance
d.
energy
____ 48. Power is measured in J per ____.
a.
watt
c.
minute
b.
hour
d.
second
____ 49. In order for work to be done, an object must ____.
a.
have mass
c.
have muscles
b.
move in the direction of the force
d.
move at a right angle to the force
____ 50. Machines let you use less force over a greater ____.
a.
distance
c.
weight
b.
mass
d.
exertion
____ 51. NO work is being done when you ____ a ball.
a.
hit
c.
carry
b.
catch
d.
drop
____ 52. When the Egyptians built the pyramids, they used the idea that a large force over a short distance can be accomplished by the same work as a small force over a ____ distance.
a.
changing
c.
shorter
b.
minimum
d.
long
____ 53. ____ describes the rate at which work is being done.
a.
Joules
c.
Effort force
b.
Power
d.
Efficiency
____ 54. A ____ is NOT a simple machine.
a.
wrench
c.
tooth
b.
shovel
d.
teeter-totter
____ 55. The pivot point of a lever is called a ____.
a.
wedge
c.
fulcrum
b.
screw
d.
wheel and axle
____ 56. Power is expressed in units of ____.
a.
light
c.
joules
b.
watts
d.
surges
____ 57. A(n) ____ is a moving inclined plane.
a.
teeter-totter
c.
elevator
b.
staircase
d.
wedge
Completion
Complete each statement.
58. When force is _________________________ to the direction of motion, no work is done.
59. A joule is equal to one ____________________ times one meter.
60. When you use a crowbar to lift a large rock, you are working against the force called ____________________.
61. Power describes the ____________________ at which work is being done.
62. Unlike a fixed pulley, a movable pulley ____________________ the input force.
63. Doorknobs and faucet handles are examples of a simple machine called a(n) ______________________________.
64. An ideal machine has an efficiency of ____________________.
65. The pivot point of a lever is called the ____________________.
66. A machine made of several simple machines is called a(n) ______________________________.
67. When a machine is used to perform a task, work output is always ____________________ than work input.
Choose the term in parentheses that correctly completes the sentence.
68. A blender is a ____________________ (simple, compound, pulley) machine.
69. The mechanical advantage that makes work easiest is one that is ____________________ (large, small, zero).
70. Holding a watermelon in your hands is an example of ____________________ (work, no work) being done.
71. A goalie stopping a hockey puck is an example of ____________________ (work, no work) being done.
72. Power does NOT depend on ____________________ (work done, muscles, time).
73. As you increase the effort distance, you ____________________ (decrease, increase, stabilize) the effort force needed.
74. The mechanical advantage tells you the number of times a machine ____________________ (increases, decreases, eliminates) the effort force.
75. A ____________________ (shovel, crowbar, potter’s wheel) is NOT an example of a lever.
76. An ideal machine has an efficiency ____________________ (less than one, equal to one, greater than one).
77. ____________________ (Heat, Friction, Work) is NOT a source of energy loss in a machine.
Matching
Match each term with the following questions.
a.
input force
d.
output force
b.
efficiency
e.
compound machine
c.
mechanical advantage
____ 78. ratio of output force to input force
____ 79. force you apply to a simple machine
____ 80. force you overcome when using a simple machine
____ 81. device made of more than one simple machine
____ 82. ability of a machine to convert work input into work output
Match each simple machine with the machines below.
a.
inclined plane
d.
lever
b.
wedge
e.
wheel and axle
c.
screw
____ 83. knife
____ 84. leaf rake
____ 85. wheelchair ramp
____ 86. potter's wheel
____ 87. threaded bolt
Match each item with the correct description below.
a.
simple machine
j.
watt
b.
work
k.
ideal machine
c.
input force
l.
screw
d.
inclined plane
m.
pulley
e.
joule
n.
mechanical advantage
f.
output force
o.
efficiency
g.
power
p.
fulcrum
h.
machine
q.
wheel and axle
i.
friction
r.
wedge
____ 88. a device that makes work easier by changing the size or direction of the applied force
____ 89. SI unit for work
____ 90. causes the output work of a machine to be less than the input work
____ 91. the rate at which work is being done
____ 92. the ratio of the output force to the input force
____ 93. a moving inclined plane
____ 94. has only one movement
____ 95. the unit of measurement of power
____ 96. two rigidly attached wheels that rotate together
____ 97. a sloped surface
____ 98. exertion of a force on an object that produces motion in the direction of the force
____ 99. the force a machine exerts
____ 100. a machine’s ability to convert work input into work output
____ 101. machine with 100% efficiency
____ 102. the pivot point of a lever
____ 103. an inclined plane wrapped around a shaft
____ 104. a grooved wheel that redirects force using a rope
____ 105. the effort force you exert
Short Answer
106.
Explain how a wheel and axle works and give examples of objects that use a wheel and axle.
107.
Sharon wants to know if friction will affect the efficiency of a ramp that she built. She will form a hypothesis and then test it.
Part A Write a hypothesis that Sharon can test.
Part B Write a plan that shows how Sharon can test her hypothesis.
108.
What does work depend on in scientific terms?
109.
You swing a rope in a circle. Are you doing work on the rope? Why or why not?
110.
Which one of the following could be the mechanical advantage of a third-class lever: 0.7, 1.5, 10.5, or 3.0? Explain your answer.
111.
An inventor claims to have built a machine that can produce 120 J of work with an input of 110 J. Would you believe the inventor's claim? Why or why not?
112.
Explain why tin snips, designed for cutting metal, have long handles and short blades.
113.
How are work, time, and power related?
114.
Gears are modified wheel-and-axle machines. Explain how to calculate the mechanical advantage of a pair of gears.
115.
A 700-watt gasoline engine and a 300-watt electric motor both do 3 J of work. Which machine can do the work faster? Explain your answer.
116.
How does low air pressure in bicycle tires reduce the efficiency of a bicycle?
117.
Give one example of a compound machine and list the simple machines that make it up.
118.
Do machines make work easier? Explain your answer.
119.
How does oil reduce friction between two surfaces?
120.
Explain how your teeth work as a wedge.
121.
Explain the transfer of energy during work.
Complete the table below by calculating the missing values. Then answer the following questions.
Situation
Force
Distance
Time
Work
Power
1. A
200 N
50 m
10 s
2. B
100 N
6 m
200 W
3. C
200 N
100 m
10 s
4. D
200 N
10 s
5000 J
122. What are the missing values in line 1?
123. What are the missing values in line 2?
124. What are the missing values in line 3?
125. What are the missing values in line 4?
126. In which situation was the most work done?
127. In which situation was the most power used?
128. How does the work done in situation D compare to that done in situation A?
129. How does the distance in situation D compare to the distance in situation A?
130. What would happen to the power in situation C if the time doubled?
131. Compare and contrast simple and compound machines.
132. Compare and contrast a screw and a wedge.
133. What is the work done in using a force of 200 N to push a box 15 m?
134. What is the power used if it took 2,000 J to move a box in 8 s?
135. What is the mechanical advantage of using a machine if you use an input force of 25 N to overcome an output force of 125 N?
136. If an output force of 50 N is used to move an object a distance of 20 m, what distance must the object be moved if the input force is 10 N, so that work in = work out?
137. What is the efficiency of a machine if the work input is 75 N and the work output is 25 N?
Problem
138.
You use 200 N of force to push a snow shovel 10 m along the ground. How much work was done?
139.
A painter lifts a 3 kg can of paint 3 m above the floor. How much work was done?
140.
How much power is needed to do 1,000 J of work on a box if it takes 50 s to lift it?
141.
How much work is done if 500 W of power is used over 2 min?
142.
Calculate the mechanical advantage of a lever where 5 N of input force is needed to move a 10 N box using that lever.
143.
A carpenter uses a claw hammer to pull a nail from a board. The nail has a resistance of 1,500 N. The carpenter applies a force of 150 N. What is the mechanical advantage of the hammer?
Essay
144. Name the six types of simple machines and give an example of each, or what each might be used to do.
145. Explain why applying force to an object does not always result in work being done.
146. Even though work input should equal work output, explain why, other than on ideal machines, machines have an efficiency less than one.
147. If a machine cannot have more work output than work input, what advantage is there to using one?
148. Compare and contrast fixed pulleys with movable pulleys and pulley systems and discuss their respective mechanical advantages.
7th Grade - CHpater 5 ONLINE REVIEW
Answer Section
TRUE/FALSE
1. ANS: T PTS: 1 DIF: Webb's I OBJ: 1/1
STA: SC.C.2.3.4
2. ANS: F PTS: 1 DIF: Webb's I OBJ: 1/1
STA: SC.C.2.3.3
3. ANS: T PTS: 1 DIF: Webb's I OBJ: 2/1
4. ANS: T PTS: 1 DIF: Webb's I OBJ: 2/1
5. ANS: F PTS: 1 DIF: Webb's I OBJ: 5/2
STA: SC.C.2.3.3 SC.C.2.3.4
6. ANS: T PTS: 1 DIF: Webb's I OBJ: 3/1
STA: SC.C.2.3.3
7. ANS: T PTS: 1 DIF: Webb's I OBJ: 3/1
8. ANS: T PTS: 1 DIF: Webb's I OBJ: 4/2
STA: SC.C.2.3.4
9. ANS: F PTS: 1 DIF: Webb's I OBJ: 7/3
10. ANS: T PTS: 1 DIF: Webb's I OBJ: 8/3
STA: SC.C.2.3.4
11. ANS: F PTS: 1
12. ANS: F PTS: 1
13. ANS: T PTS: 1
14. ANS: T PTS: 1
15. ANS: T PTS: 1
MULTIPLE CHOICE
16. ANS: C PTS: 1 DIF: Webb's I STA: SC.C.2.3.4
17. ANS: B PTS: 1 DIF: Webb's I STA: SC.C.2.3.2 SC.C.2.3.3
18. ANS: D PTS: 1 DIF: Webb's I STA: SC.C.2.3.6
19. ANS: D PTS: 1 DIF: Webb's I STA: SC.C.2.3.4
20. ANS: B PTS: 1 DIF: Webb's II STA: SC.C.2.3.2
21. ANS: C PTS: 1 DIF: Webb's II STA: SC.C.2.3.6
22. ANS: B PTS: 1 DIF: Webb's II STA: SC.C.2.3.4
23. ANS: A PTS: 1 DIF: Webb's II STA: SC.C.2.3.4
24. ANS: B PTS: 1 DIF: Webb's II STA: SC.C.2.3.3 SC.C.2.3.4
25. ANS: D PTS: 1 DIF: Webb's I STA: SC.C.2.3.4
26. ANS: B PTS: 1 DIF: Webb's II STA: SC.C.2.3.4
27. ANS: C PTS: 1 DIF: Webb's II STA: SC.C.1.3.1
28. ANS: C PTS: 1 DIF: Webb's II STA: SC.C.2.3.2
29. ANS: A PTS: 1 DIF: Webb's II OBJ: 1/1
STA: SC.C.2.3.7
30. ANS: C PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
31. ANS: C PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
32. ANS: C PTS: 1 DIF: Webb's I OBJ: 4/2
STA: SC.C.2.3.4
33. ANS: B PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
34. ANS: D PTS: 1 DIF: Webb's I OBJ: 3/1
35. ANS: A PTS: 1 DIF: Webb's I OBJ: 5/2
36. ANS: C PTS: 1 DIF: Webb's I OBJ: 5/2
STA: SC.C.2.3.4
37. ANS: D PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
38. ANS: C PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
39. ANS: A PTS: 1 DIF: Webb's I OBJ: 5/2
STA: SC.C.2.3.4
40. ANS: B PTS: 1 DIF: Webb's I OBJ: 7/3
41. ANS: A PTS: 1 DIF: Webb's I OBJ: 7/3
42. ANS: C PTS: 1 DIF: Webb's I OBJ: 5/2
STA: SC.C.2.3.4
43. ANS: C PTS: 1 DIF: Webb's II OBJ: 7/3
STA: SC.C.2.3.4
44. ANS: B PTS: 1
45. ANS: A PTS: 1
46. ANS: D PTS: 1
47. ANS: B PTS: 1
48. ANS: D PTS: 1
49. ANS: B PTS: 1
50. ANS: A PTS: 1
51. ANS: C PTS: 1
52. ANS: D PTS: 1
53. ANS: B PTS: 1
54. ANS: A PTS: 1
55. ANS: C PTS: 1
56. ANS: B PTS: 1
57. ANS: D PTS: 1
COMPLETION
58. ANS: perpendicular
PTS: 1 DIF: Webb's I OBJ: 1/1 STA: SC.C.2.3.3
59. ANS: newton
PTS: 1 DIF: Webb's I OBJ: 2/1
60. ANS: gravity
PTS: 1 DIF: Webb's I OBJ: 1/1 STA: SC.C.2.3.1 SC.C.2.3.3 SC.C.2.3.4
61. ANS: rate
PTS: 1 DIF: Webb's I OBJ: 3/1
62. ANS: multiplies
PTS: 1 DIF: Webb's I OBJ: 7/3 STA: SC.C.2.3.4
63. ANS: wheel and axle
PTS: 1 DIF: Webb's I OBJ: 7/3 STA: SC.C.2.3.4
64. ANS: 100 percent
PTS: 1 DIF: Webb's I OBJ: 5/2 STA: SC.C.2.3.4
65. ANS: fulcrum
PTS: 1 DIF: Webb's I OBJ: 7/3
66. ANS: compound machine
PTS: 1 DIF: Webb's I OBJ: 7/3
67. ANS:
smaller
less
PTS: 1 DIF: Webb's I OBJ: 5/2 STA: SC.C.2.3.4
68. ANS: compound
PTS: 1
69. ANS: large
PTS: 1
70. ANS: no work
PTS: 1
71. ANS: work
PTS: 1
72. ANS: muscles
PTS: 1
73. ANS: decrease
PTS: 1
74. ANS: increases
PTS: 1
75. ANS: potter’s wheel
PTS: 1
76. ANS: equal to one
PTS: 1
77. ANS: Work
PTS: 1
MATCHING
78. ANS: C PTS: 1 DIF: Webb's I OBJ: 5/2
79. ANS: A PTS: 1 DIF: Webb's I OBJ: 5/2
STA: SC.C.2.3.4
80. ANS: D PTS: 1 DIF: Webb's I OBJ: 5/2
STA: SC.C.2.3.4
81. ANS: E PTS: 1 DIF: Webb's I OBJ: 7/3
82. ANS: B PTS: 1 DIF: Webb's I OBJ: 5/2
STA: SC.C.2.3.4
83. ANS: B PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
84. ANS: D PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
85. ANS: A PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
86. ANS: E PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
87. ANS: C PTS: 1 DIF: Webb's I OBJ: 7/3
STA: SC.C.2.3.4
88. ANS: H PTS: 1
89. ANS: E PTS: 1
90. ANS: I PTS: 1
91. ANS: G PTS: 1
92. ANS: N PTS: 1
93. ANS: R PTS: 1
94. ANS: A PTS: 1
95. ANS: J PTS: 1
96. ANS: Q PTS: 1
97. ANS: D PTS: 1
98. ANS: B PTS: 1
99. ANS: F PTS: 1
100. ANS: O PTS: 1
101. ANS: K PTS: 1
102. ANS: P PTS: 1
103. ANS: L PTS: 1
104. ANS: M PTS: 1
105. ANS: C PTS: 1
SHORT ANSWER
106. ANS:
A wheel and axle is composed of two circular objects of different diameters that are attached so that they rotate together. Examples of a wheel and axle where a force is used to turn the axle are a fan or a Ferris wheel. Examples where a force is used to turn the wheel are a doorknob or a steering wheel.
PTS: 1 DIF: Webb's II STA: SC.C.2.3.4
107. ANS:
Part A Hypotheses will vary, but a possible one is “Friction will affect the efficiency of a ramp. It will slow down objects traveling on the ramp.”
Part B Plans will vary, but a possible one includes setting up two ramps that are identical in length, height, and smooth material for the surface. The only difference is that one ramp (the control) will have nothing on the smooth surface, and the other ramp (the variable) will have a rough material such as sandpaper, carpet, or cloth covering the ramp’s smooth surface. Objects moving down the ramps will be timed and the results recorded. Repeated trials are suggested so that the results are more reliable.
PTS: 1 DIF: Webb's III STA: SC.C.2.3.2 SC.C.2.3.5 SC.C.2.3.6
108. ANS:
Work depends on the force applied to the object and the distance the object is moved.
PTS: 1 DIF: Webb's II OBJ: 1/1
109. ANS:
No, the force applied to the rope is not in the same direction as the motion of the rope.
PTS: 1 DIF: Webb's II OBJ: 1/1
110. ANS:
0.7, because the mechanical advantage of a third-class lever is always less than one.
PTS: 1 DIF: Webb's II OBJ: 5/2 STA: SC.C.2.3.4
111. ANS:
No. The machine would have an efficiency of 108%. This is not possible since machines cannot have an efficiency greater than 100%.
PTS: 1 DIF: Webb's II OBJ: 5/2 STA: SC.C.2.3.4
112. ANS:
The mechanical advantage for scissors, a first-class lever, is the length of the handle divided by the length of the blade. Cutting hard materials requires a high mechanical advantage.
PTS: 1 DIF: Webb's II OBJ: 5/2
113. ANS:
Power is the measure of work done per unit of time.
PTS: 1 DIF: Webb's II OBJ: 3/1
114. ANS:
Divide the radius of the wheel by the radius of the axle.
PTS: 1 DIF: Webb's II OBJ: 8/3 STA: SC.C.2.3.4
115. ANS:
The 700-watt engine does the work faster because it takes a smaller amount of time to do the work.
PTS: 1 DIF: Webb's II OBJ: 2/1
116. ANS:
Low air increases the friction between the tire and the road. This reduces efficiency.
PTS: 1 DIF: Webb's II OBJ: 5/2 STA: SC.C.2.3.2
117. ANS:
Sample answer: a lawnmower is made up of a lever, wheel and axle, and wedge.
PTS: 1 DIF: Webb's II OBJ: 7/3
118. ANS:
Machines do not change the amount of work needed to do something. They just allow you to use less force over a longer distance.
PTS: 1 DIF: Webb's II OBJ: 1/1 STA: SC.C.2.3.4
119. ANS:
Oil fills the gaps between surfaces and prevents many spots on the surfaces from coming in contact, reducing the force of friction.
PTS: 1 DIF: Webb's II OBJ: 6/2 STA: SC.C.2.3.2
120. ANS:
A wedge changes the direction of applied force. When you push your teeth into an apple the downward effort force is changed to a sideways force that pushes the apple apart.
PTS: 1 DIF: Webb's II OBJ: 1/1 STA: SC.C.2.3.4
121. ANS:
When something is moving it has kinetic energy. By lifting an object you increase its potential energy. As you perform work, energy is transferred from you to the object you are working on.
PTS: 1 DIF: Webb's II OBJ: 3/1 STA: SC.C.2.3.5
122. ANS:
10,000 J; 1,000 W
PTS: 1
123. ANS:
3 s; 600 J
PTS: 1
124. ANS:
20,000 J; 2,000 W
PTS: 1
125. ANS:
25 m; 500 W
PTS: 1
126. ANS:
C
PTS: 1
127. ANS:
C
PTS: 1
128. ANS:
Half as much work is done.
PTS: 1
129. ANS:
It is half as far.
PTS: 1
130. ANS:
The power would be half as much.
PTS: 1
131. ANS:
A simple machine has only one movement. A compound machine is made up of two or more simple machines. Both make work easier by changing the size or direction of the force applied to an object to do work.
PTS: 1
132. ANS:
Both are inclined planes. A screw is an inclined plane wrapped around a cylinder. A wedge is an inclined plane that moves.
PTS: 1
133. ANS:
W = F ´ d = 200 ´ 15 = 3,000 J
PTS: 1
134. ANS:
PTS: 1
135. ANS:
PTS: 1
136. ANS:
PTS: 1
137. ANS:
PTS: 1
PROBLEM
138. ANS:
W = F ´ d = 200 N ´ 10 m = 2,000 J
PTS: 1 DIF: Webb's II OBJ: 2/1 STA: SC.C.2.3.2
139. ANS:
W = m ´ g ´ d = 3 kg ´ 9.8 m/s2 ´ 3 m = 88 J
PTS: 1 DIF: Webb's II OBJ: 2/1
140. ANS:
P = W/t = 1,000 J/50 s = 20 W
PTS: 1 DIF: Webb's II OBJ: 3/1
141. ANS:
W = P ´ t = 500 W ´ 120 s = 60,000 J
PTS: 1 DIF: Webb's II OBJ: 3/1
142. ANS:
M.A. = Resistance Force/Force = 10 N/5 N = 2
PTS: 1 DIF: Webb's II OBJ: 5/2 STA: SC.C.2.3.4
143. ANS:
M.A. = Resistance Force/Force = 1,500 N/150 N = 10
PTS: 1 DIF: Webb's II OBJ: 3/1 STA: SC.C.2.3.4
ESSAY
144. ANS:
1. inclined plane—ramp to move furniture onto truck
2. wedge—axe, knife blade
3. screw—base of lightbulb, jar lid
4. lever—wheelbarrow, shovel, jack to lift car to change tire
5. wheel and axle—steering wheel, door knob, electric pencil sharpener
6. pulley—window blinds, drapes, painters’ scaffolds
PTS: 1
145. ANS:
The object may not move. The object must move in the direction of the applied force in order for work to be done.
PTS: 1
146. ANS:
Energy, therefore work, is lost due to heat loss and friction in a machine.
PTS: 1
147. ANS:
A machine makes work easier by changing the amount of force you need to exert, the distance over which the force is exerted, or the direction in which you exert your force.
PTS: 1
148. ANS:
A fixed pulley changes the direction in which a force is exerted and has a mechanical advantage of 1. A movable pulley attached to the object being lifted allows for the exertion of a smaller force to lift the object. The mechanical advantage of a movable pulley is 2. A pulley system is a combination of fixed and movable pulleys and has a mechanical advantage equal to the number of sections of rope pulling on the object.
PTS: 1
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