Transcript Ch. 5 Work and Energy Review

Ch. 5 Work and Energy
Review
1
• In which of the following actions is work
not being done on the underlined object?
• A. A hammer strikes the head of a nail and drives
the nail into a board.
• B. A flowerpot falls off a window ledge.
• C. A baseball strikes the side of a car, making a
permanent dent in the metal.
• D. After stubbing a toe, a person leans against a
tree trunk in order to rub the toe.
2
• How much work is being done on a couch when
it is pushed 11.5 m by a force of 326 N at an
angle of 20.0° above the horizontal?
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A. 3520 J
B. 3749 J
C. 1280 J
D. 381 J
3
In which choice is negative work being done on the
underlined object?
A. The force supplied by the engine of a car
causes the car to move backward.
B. A pump exerts a force on water as the
water is pumped up a hill.
C. While in contact with the ball, a tennis
racket supplies a force that causes the
ball to move.
D. A brake supplies the force of friction that brings
a roller coaster to a stop.
4
• A box with a mass of 7.37 kg has an initial
velocity of 7.6 m/s as it slides across a surface.
If the coefficient of kinetic friction between the
box and the surface is 0.15, how far will the box
move for its velocity to decrease to 3.8 m/s?
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A. 14 m
B. 2.2 m
C. 19 m
D. -14 m
5
• As an object falls, the sum of its kinetic and
potential energy remains constant. This sum of
the potential and kinetic energy of an object is
the ____________ energy of the object.
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A. chemical
B. mechanical
C. momentum
D. nonmechanical
6
• A swinging pendulum is represented in the diagram.
Assume that no friction exists at the point that supports
the pendulum. At the numbered points in the diagram,
the mechanical energy possessed by the pendulum is
A. the same at all three points.
B. greatest at point 1.
C. greatest at point 2.
D. greatest at points 1 and 3.
7
• Suppose that a ball is launched into the air by a
pitching machine. How far above the launch
point will the ball go if it has an initial vertical
speed of 37.0 m/s?
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A. 69.8 m
B. 1.89 m
C. 685 m
D. 1.40 × 102 m
8
• You are assigned the task of moving bricks, one
at a time, from the ground to a platform that is 2
m high. Moving the first 50 bricks takes 3.5 min.
If you use more power to move the next 50
bricks, you will
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A. increase the time required.
B. decrease the time required.
C. increase the work you do.
D. decrease the work you do.
9
• A construction crane lifts a large steel beam that
weighs 12 000 N a distance of 30 m in 60 s.
Calculate the power of the crane.
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A. 6000 W
B. 21 600 000 W
C. 24 000 W
D. 6.7 W
10
• A motor with a power rating of 11.2 kW is used
to move a truck a distance of 68 m. If the total
work done on the truck is 4.85 × 106 J, how
much time does the motor require to move the
truck?
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A. 29 400 s
B. 2.31 × 10-3 s
C. 433 s
D. 13.5 s
11
• As a constant net force acts on an object
initially at rest, the KE of the object
• A. Increases
• B. Decreases
• C. Remains constant
12
• As a crane lifts a load at a constant speed
the
– PE: increases, decreases, remains constant
– KE: increases, decreases, remains constant
13
• If the velocity of a body is doubled the KE
– Doubles, halves, quadruples, quarters
• If the velocity of a body is halved the KE
– Doubles, halves, quadruples, quarters
• If the mass of a body is quartered the KE
– Doubles, halves, quadruples, quarters
14
C
D
B
E
A
A ball is thrown into the air as shown. Five positions are diagrammed.
Where does the ball have the maximum KE?
A
PE?
C
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