PreLecture Questions

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Chapter 6 Pre-Lecture Questions
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-01
Is it possible to do work on an object that
remains at rest?
1) yes 2) no
Pre-Lecture Quiz 06
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02
Pre-Lecture Quiz 06-02
A box is being pulled across a rough floor at a
constant speed. What can you say about the work
done by friction?
1) friction does no work at all 2) friction
does negative work 3) friction does positive work
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-03
Can friction ever do positive work?
1) yes 2) no
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-04
In a baseball game, the catcher stops a 90-mph
pitch. What can you say about the work done by
the catcher on the ball?

• 1) catcher has done positive work
• 2) catcher has done negative work
• 3) catcher has done zero work

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-05
A ball tied to a string is being whirled around
in a circle. What can you say about the work
done by tension?
1) tension does no work at all 2) tension does
negative work 3) tension does positive work
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-06
A box is being pulled up a rough incline by a
rope connected to a pulley. How many forces are
doing work on the box?
1) one force 2) two forces 3) three forces 4)
four forces
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-07
You lift a book with your hand in such a way that
it moves up at constant speed. While it is
moving, what is the total work done on the book?
1) mg ? ?r 2) FHAND ? ?r 3) (FHAND mg) ?
?r 4) zero
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-08
By what factor does the kinetic energy of a car
change when its speed is tripled?
1) factor of 3 2) factor of 6 3) factor of
9 4) factor of 12
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-09
Car 1 has twice the mass of car 2, but they
both have the same kinetic energy. How do their
speeds compare?
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-10
Two stones, one twice the mass of the other, are
dropped from a cliff. Just before hitting the
ground, what is the kinetic energy of the heavy
stone compared to the light one?
1) quarter as much 2) half as much 3) the
same 4) twice as much 5) four times as much
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-11
Two stones, one twice the mass of the other, are
dropped from a cliff. Just before hitting the
ground, what is the final speed of the heavy
stone compared to the light one?

• 1) quarter as much
• 2) half as much
• 3) the same
• 4) twice as much
• 5) four times as much

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-12
A child on a skateboard is moving at a speed of 2
m/s. After a force acts on the child, her speed
is 3 m/s. What can you say about the work done
by the external force on the child?

• 1) positive work was done
• 2) negative work was done
• 3) zero work was done

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-13
If a car traveling 60 km/hr can brake to a stop
within 20 m, what is its stopping distance if it
is traveling 120 km/hr? Assume that the braking
force is the same in both cases.
1) 20 m 2) 30 m 3) 40 m 4) 60 m 5) 80 m
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-14
A car starts from rest and accelerates to 30 mph.
Later, it gets on a highway and accelerates to
60 mph. Which takes more energy, the 0?30 mph,
or the 30?60 mph?
1) 0 ? 30 mph 2) 30 ? 60 mph 3) both the
same
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-15
The work W0 accelerates a car from 0 to 50 km/hr.
How much work is needed to accelerate the car
from 50 km/hr to 150 km/hr?

• 1) 2 W0
• 2) 3 W0
• 3) 6 W0
• 4) 8 W0
• 5) 9 W0

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-16
Two blocks of mass m1 and m2 (m1 gt m2) slide on a
frictionless floor and have the same kinetic
energy when they hit a long rough stretch (m gt
0), which slows them down to a stop. Which one
goes farther?
1) m1 2) m2 3) they will go the
same distance
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-17
A golfer making a putt gives the ball an initial
velocity of v0, but he has badly misjudged the
putt, and the ball only travels one-quarter of
the distance to the hole. If the resistance
force due to the grass is constant, what speed
should he have given the ball (from its original
position) in order to make it into the hole?
1) 2 v0 2) 3 v0 3) 4 v0
4) 8 v0 5) 16 v0
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-18
Is it possible for the kinetic energy of an
object to be negative?

• 1) yes
• 2) no

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-19
Is it possible for the gravitational potential
energy of an object to be negative?

• 1) yes
• 2) no

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-20
You and your friend both solve a problem
involving a skier going down a slope, starting
from rest. The two of you have chosen different
levels for y 0 in this problem. Which of the
following quantities will you and your friend
agree on?
I) skiers PE II) skiers change in PE
III) skiers final KE

• 1) only II
• 2) only III
• 3) I, II, and III
• 4) only I and III
• 5) only II and III

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-21
Two paths lead to the top of a big hill. One is
steep and direct, while the other is twice as
long but less steep. How much more potential
energy would you gain if you take the longer path?
1) the same 2) twice as much 3) four times as
much 4) half as much 5) you gain no PE in
either case
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-22
How does the work required to stretch a spring 2
cm compare with the work required to stretch it 1
cm?

• 1) same amount of work
• 2) twice the work
• 3) 4 times the work
• 4) 8 times the work

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-23
A mass attached to a vertical spring causes the
spring to stretch and the mass to move downwards.
What can you say about the springs potential
energy (PEs) and the gravitational potential
energy (PEg) of the mass?

• 1) both PEs and PEg decrease
• 2) PEs increases and PEg decreases
• 3) both PEs and PEg increase
• 4) PEs decreases and PEg increases
• 5) PEs increases and PEg is constant

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-24
Three balls of equal mass start from rest and
roll down different ramps. All ramps have the
same height. Which ball has the greater speed at
the bottom of its ramp?
2
3
1
4) same speed for all balls
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-25
A truck, initially at rest, rolls down a
frictionless hill and attains a speed v at the
bottom. To achieve a speed 2v at the bottom, how
many times higher must the hill be?
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-26
A box sliding on a frictionless flat surface runs
into a fixed spring, which compresses a distance
x to stop the box. If the initial speed of the
box were doubled, how much would the spring
compress in this case?
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-27
Paul and Kathleen start from rest at the same
time on frictionless water slides with different
shapes. At the bottom, whose velocity is greater?
1) Paul 2) Kathleen 3) both the same
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-28
Paul and Kathleen start from rest at the same
time on frictionless water slides with different
shapes. Who makes it to the bottom first?
1) Paul 2) Kathleen 3) both the same
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-29
A cart starting from rest rolls down a hill and
at the bottom has a speed of 4 m/s. If the cart
were given an initial push, so its initial speed
at the top of the hill was 3 m/s, what would be
its speed at the bottom?
1) 4 m/s 2) 5 m/s 3) 6 m/s 4) 7 m/s
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-30
You see a leaf falling to the ground with
constant speed. When you first notice it, the
leaf has initial total energy PEi KEi. You
watch the leaf until just before it hits the
ground, at which point it has final total energy
PEf KEf. How do these total energies compare?

• 1) PEi KEi gt PEf KEf
• 2) PEi KEi PEf KEf
• 3) PEi KEi lt PEf KEf
• 4) impossible to tell from the information
  provided

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-31
You throw a ball straight up into the air. In
addition to gravity, the ball feels a force due
to air resistance. Compared to the time it
takes the ball to go up, the time it takes to
come back down is
1) smaller 2) the same 3) greater
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-32
Mike applied 10 N of force over 3 m in 10
seconds. Joe applied the same force over the
same distance in 1 minute. Who did more work?
1) Mike 2) Joe 3) both did the same work
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-33
Mike performed 5 J of work in 10 s. Joe did 3 J
of work in 5 s. Who produced the greater power?

• 1) Mike produced more power
• 2) Joe produced more power
• 3) both produced the same amount of power

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-34
Engine 1 produces twice the power of engine 2.
Can we conclude that engine 1 does twice as
much work as engine 2?

• 1) yes
• 2) no

Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-35
When you pay the electric company by the
kilowatt-hour, what are you actually paying for?
1) energy 2) power 3) current 4) voltage
Pre-Lecture Quiz 06
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Pre-Lecture Quiz 06-36
Which contributes more to the cost of your
electric bill each month, a 1500-Watt hair dryer
or a 600-Watt microwave oven?
1) hair dryer 2) microwave oven 3) both
contribute equally 4) depends upon what you cook
in the oven 5) depends upon how long each one is
on
Pre-Lecture Quiz 06
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