Examples
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Problems |
Assistance |
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1-4 |
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6-10 |
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11-15 |
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16-20 |
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21-24 |
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26-30 |
Problem 1
In what ways is the word “work” as used in everyday language the same as that defined in physics?
In what ways is it different?
Give examples of both.
Problem 2
Can a centripetal force ever do work on an object? Explain.
Problem 3
Can the normal force on an object ever do work? Explain.
Problem 4
A woman swimming upstream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely
floats, is work done on her?
Problem 6
Why is it tiring to push hard against a solid wall even though you are doing no work?
Problem 7
What
is the correct unit of work expressed in SI units?
A) kg
m/s2
B) kg
m2/s
C) kg
m2/s2
D) kg2 m/s2
Problem 8
Can work be done on a system if there is no motion?
A) Yes, if an outside force is provided.
B) Yes, since motion is only relative.
C) No, since a system which is not moving has no
energy.
D) No, because of the way work is defined.
Problem 9
If you push twice as hard against a stationary brick
wall, the amount of work you do
A) doubles.
B) is cut in half.
C) remains constant but non-zero.
D) remains constant at zero.
Prob
A 50-N object was lifted 2.0 m vertically and is being
held there. How much work is
being done in holding the box in this position?
A) more than 100 J
B) 100 J
C) less than 100 J, but more than 0 J
D) 0 J
Problem 11
If you walk
5.0 m horizontally forward at a constant velocity carrying a 10-N object,
the amount of work you do is
A) more than 50 J.
B) equal to 50 J.
C) less than 50 J, but more than 0 J.
D) zero.
A container of water is lifted vertically 3.0 m then
returned to its original position.
If the total weight is 30 N, how much work was done?
A) 45 J
B) 90 J
C) 180 J
D) No work was done.
Problem 13
Does the centripetal force acting on an object do work
on the object?
A) Yes, since a force acts and the object moves, and
work is force times distance.
B) Yes, since it takes energy to turn an object.
C) No, because the object has constant speed.
D) No, because the force and the displacement of the
object are perpendicular.
Problem 14
You throw a ball straight up.
Compare the sign of the work done by gravity while the ball goes up
with the sign of the work done by gravity while it goes down.
A) Work is + on the way up and + on the way down.
B) Work is + on the way up and - on the way down.
C) Work is - on the way up and + on the way down.
D) Work is - on the way up and - on the way down.
Problem 15
The area under the curve, on a Force versus position
(F vs. x) graph, represents
A) work.
B) kinetic energy.
C) power.
D) potential energy.
Problem 16
On a plot of Force versus position (F vs. x), what
represents the work done by the force F?
A) the slope of the curve
B) the length of the curve
C) the area under the curve
D) the product of the maximum force times the maximum
x
Problem 17
The quantity 1/2 mv2 is
A) the kinetic energy of the object.
B) the potential energy of the object.
C) the work done on the object by the force.
D) the power supplied to the object by the force.
If the net work done on an object is positive, then
the object's kinetic energy
A) decreases.
B) remains the same.
C) increases.
D) is zero.
Problem 19
If the net work done on an object is negative, then
the object's kinetic energy
A) decreases.
B) remains the same.
C) increases.
D) is zero.
Problem 20
If the net work done on an object is zero, then the
object's kinetic energy
A) decreases.
B) remains the same.
C) increases.
D) is zero.
Problem 21
A truck weighs twice as much as a car, and is moving
at twice the speed of the car.
Which statement is true about the truck's kinetic energy compared to that of
the car?
A) All that can be said is that the truck has more
kinetic energy.
B) The truck has twice the kinetic energy of the car.
C) The truck has 4 times the kinetic energy of the
car.
D) The truck has 8 times the kinetic energy of the
car.
Problem 22
A brick is moving at a speed of 3 m/s and a pebble is
moving at a speed of 5 m/s. If
both objects have the same kinetic energy, what is the ratio of the brick's
mass to the rock's mass?
A) 25 to 9
B) 5 to 3
C) 12.5 to 4.5
D) 3 to 5
A 4.0-kg mass is moving with speed 2.0 m/s.
A 1.0-kg mass is moving with speed 4.0 m/s.
Both objects encounter the same constant braking force, and are
brought to rest. Which object
travels the greater distance before stopping?
A) the 4.0-kg mass
B) the 1.0-kg mass
C) Both travel the same distance.
D) cannot be determined from the information given
You slam on the brakes of your car in a panic, and
skid a certain distance on a straight, level road.
If you had been traveling twice as fast, what distance would the car
have skidded, under the same conditions?
A) It would have skidded 4 times farther.
B) It would have skidded twice as far.
C) It would have skidded 1.4 times farther.
D) It is impossible to tell from the information
given.
State the work-energy principle.
The quantity mgy is
A) the kinetic energy of the object.
B) the gravitational potential energy of the object.
C) the work done on the object by the force.
D) the power supplied to the object by the force.
The quantity 1/2 kx2 is
A) the kinetic energy of the object.
B) the elastic potential energy of the object.
C) the work done on the object by the force.
D) the power supplied to the object by the force.
Is it possible for a system to have negative potential
energy?
A) Yes, as long as the total energy is positive.
B) Yes, since the choice of the zero of potential
energy is arbitrary.
C) No, because the kinetic energy of a system must
equal its potential energy.
D) No, because this would have no physical meaning.
An object is released from rest a height h above
the ground. A second object with
four times the mass of the first if released from the same height.
The potential energy of the second object compared to the first is
A) one-fourth as much.
B) one-half as much.
C) twice as much.
D) four times as much.