Cutnell/Johnson Physics 7th edition

1
Cutnell/JohnsonPhysics 7th edition

• Classroom Response System Questions

Chapter 4 Forces and Newtons Laws of Motion
Interactive Lecture Questions
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4.2.1. A pipe is bent into the shape shown and
oriented so that it is sitting horizontally on a
table top. You are looking at the pipe from
above. The interior of the pipe is smooth. A
marble is shot into one end and exits the other
end. Which one of the paths shown in the drawing
will the marble follow when it leaves the
pipe? a) 1 b) 2 c) 3 d) 4 e) 5
3
4.2.1. A pipe is bent into the shape shown and
oriented so that it is sitting horizontally on a
table top. You are looking at the pipe from
above. The interior of the pipe is smooth. A
marble is shot into one end and exits the other
end. Which one of the paths shown in the drawing
will the marble follow when it leaves the
pipe? a) 1 b) 2 c) 3 d) 4 e) 5
4
4.2.2. If an object is moving can you conclude
there are forces acting on it? If an object is
at rest, can you conclude there are no forces
acting on it? Consider each of the following
situations. In which one of the following cases,
if any, are there no forces acting on the
object? a) A bolt that came loose from a
satellite orbits the earth at a constant
speed. b) After a gust of wind has blown
through a tree, an apple falls to the ground. c)
A man rests by leaning against a tall building
in downtown Dallas. d) Sometime after her
parachute opened, the sky diver fell toward the
ground at a constant velocity. e) Forces are
acting on all of the objects in choices a, b, c,
and d.
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4.2.2. If an object is moving can you conclude
there are forces acting on it? If an object is
at rest, can you conclude there are no forces
acting on it? Consider each of the following
situations. In which one of the following cases,
if any, are there no forces acting on the
object? a) A bolt that came loose from a
satellite orbits the earth at a constant
speed. b) After a gust of wind has blown
through a tree, an apple falls to the ground. c)
A man rests by leaning against a tall building
in downtown Dallas. d) Sometime after her
parachute opened, the sky diver fell toward the
ground at a constant velocity. e) Forces are
acting on all of the objects in choices a, b, c,
and d.
6
4.2.3. A child is driving a bumper car at an
amusement park. During one interval of the ride,
she is traveling at the cars maximum speed when
she crashes into a bumper attached to one of the
side walls. During the collision, her glasses
fly forward from her face. Which of the
following statements best describes why the
glasses flew from her face? a) The glasses
continued moving forward because there was too
little force acting on them to hold them on her
face during the collision. b) During the
collision, the girls face pushed the glasses
forward. c) The glasses continued moving
forward because the force of the air on them was
less than the force of the girls face on
them. d) During the collision, the car pushed
the girl forward causing her glasses to fly off
her face. e) During the collision, the wall
pushed the car backward and the girl reacted by
pushing her glasses forward.
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4.2.3. A child is driving a bumper car at an
amusement park. During one interval of the ride,
she is traveling at the cars maximum speed when
she crashes into a bumper attached to one of the
side walls. During the collision, her glasses
fly forward from her face. Which of the
following statements best describes why the
glasses flew from her face? a) The glasses
continued moving forward because there was too
little force acting on them to hold them on her
face during the collision. b) During the
collision, the girls face pushed the glasses
forward. c) The glasses continued moving
forward because the force of the air on them was
less than the force of the girls face on
them. d) During the collision, the car pushed
the girl forward causing her glasses to fly off
her face. e) During the collision, the wall
pushed the car backward and the girl reacted by
pushing her glasses forward.
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4.3.1. A car of mass m is moving at a speed 3v in
the left lane on a highway. In the right lane, a
truck of mass 3m is moving at a speed v. As the
car is passing the truck, the driver notices that
the traffic light ahead has turned yellow. Both
drivers apply the brakes to stop ahead. What is
the ratio of the force required to stop the truck
to that required to stop the car? Assume each
vehicle stops with a constant deceleration and
stops in the same distance x. a) 1/9 b)
1/3 c) 1 d) 3 e) 9
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4.3.1. A car of mass m is moving at a speed 3v in
the left lane on a highway. In the right lane, a
truck of mass 3m is moving at a speed v. As the
car is passing the truck, the driver notices that
the traffic light ahead has turned yellow. Both
drivers apply the brakes to stop ahead. What is
the ratio of the force required to stop the truck
to that required to stop the car? Assume each
vehicle stops with a constant deceleration and
stops in the same distance x. a) 1/9 b)
1/3 c) 1 d) 3 e) 9
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4.3.2. A car is driving due south through a
parking lot and its speed is monitored. Prepare
a graph of the cars speed versus time using the
following data Segment A the car begins at
rest and uniformly accelerates to 5 m/s in an
elapsed time of 2 s. Segment B for the next 10
seconds, the car moves at a constant speed of 5
m/s. Segment C during the next 2 seconds, the
car uniformly slows to 3 m/s. Segment D for the
next 4 seconds, the car travels at a constant
speed of 3 m/s. Using your graph, determine which
one of the following statements is false. a)
Net forces act on the car during intervals A and
C. b) No net force acts on the car during
interval B. c) Opposing forces may be acting on
the car during interval C. d) The magnitude of
the net force acting during interval A is less
than that during C. e) Opposing forces may be
acting on the car during interval B.
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4.3.2. A car is driving due south through a
parking lot and its speed is monitored. Prepare
a graph of the cars speed versus time using the
following data Segment A the car begins at
rest and uniformly accelerates to 5 m/s in an
elapsed time of 2 s. Segment B for the next 10
seconds, the car moves at a constant speed of 5
m/s. Segment C during the next 2 seconds, the
car uniformly slows to 3 m/s. Segment D for the
next 4 seconds, the car travels at a constant
speed of 3 m/s. Using your graph, determine which
one of the following statements is false. a)
Net forces act on the car during intervals A and
C. b) No net force acts on the car during
interval B. c) Opposing forces may be acting on
the car during interval C. d) The magnitude of
the net force acting during interval A is less
than that during C. e) Opposing forces may be
acting on the car during interval B.
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4.3.3 The graph shows the velocities of two
objects as a function of time. During the
intervals A, B, and C indicated, net forces
, , and act on the two
objects, respectively. If the objects have equal
mass, which one of the following choices is the
correct relationship between the magnitudes of
the three net forces? a) FA gt FB FC b) FC gt
FA gt FB c) FA lt FB lt FC d) FA FB FC e)
FA FC gt FB
13
4.3.3 The graph shows the velocities of two
objects as a function of time. During the
intervals A, B, and C indicated, net forces
, , and act on the two
objects, respectively. If the objects have equal
mass, which one of the following choices is the
correct relationship between the magnitudes of
the three net forces? a) FA gt FB FC b) FC gt
FA gt FB c) FA lt FB lt FC d) FA FB FC e)
FA FC gt FB
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4.3.4. The drawing shows a steel ball flying at
constant velocity from point A to point B in a
region of space where the effects of gravity are
negligible. During the short time that passes as
the ball flies past point B, a magnet exerts a
force on it in the direction of the magnet.
Which of the following trajectories does the ball
follow beyond point B? a) 1 b) 2 c) 3 d)
4 e) 5
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4.3.4. The drawing shows a steel ball flying at
constant velocity from point A to point B in a
region of space where the effects of gravity are
negligible. During the short time that passes as
the ball flies past point B, a magnet exerts a
force on it in the direction of the magnet.
Which of the following trajectories does the ball
follow beyond point B? a) 1 b) 2 c) 3 d)
4 e) 5
16
4.3.5. A 912-kg car is being driven down a
straight, level road at a constant speed of 31.5
m/s. When the driver sees a police cruiser
ahead, she removes her foot from the accelerator.
After 8.00 s, the speed of the car is 24.6 m/s,
which is the posted speed limit. What is the
magnitude of the average net force acting on the
car during the 8.00 s interval? a) 55.2 N b)
445 N c) 629 N d) 787 N e) 864 N
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4.3.5. A 912-kg car is being driven down a
straight, level road at a constant speed of 31.5
m/s. When the driver sees a police cruiser
ahead, she removes her foot from the accelerator.
After 8.00 s, the speed of the car is 24.6 m/s,
which is the posted speed limit. What is the
magnitude of the average net force acting on the
car during the 8.00 s interval? a) 55.2 N b)
445 N c) 629 N d) 787 N e) 864 N
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4.4.1. An object is moving due south at a
constant velocity. Then, a net force directed
due west acts on the object for a short time
interval, after which, the net force on the
object is zero newtons. Which one of the
following statements concerning the object is
necessarily true? a) The final velocity of the
object will be directed south of west. b) The
final velocity of the object will be directed due
south. c) The direction of acceleration of the
object while the force was being applied was
south of west. d) The magnitude of the objects
acceleration while the force was being applied
was dependent on the objects initial
velocity. e) The change in the objects
velocity while the force was applied was directed
south of east.
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4.4.1. An object is moving due south at a
constant velocity. Then, a net force directed
due west acts on the object for a short time
interval, after which, the net force on the
object is zero newtons. Which one of the
following statements concerning the object is
necessarily true? a) The final velocity of the
object will be directed south of west. b) The
final velocity of the object will be directed due
south. c) The direction of acceleration of the
object while the force was being applied was
south of west. d) The magnitude of the objects
acceleration while the force was being applied
was dependent on the objects initial
velocity. e) The change in the objects
velocity while the force was applied was directed
south of east.
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4.5.1. A water skier is being pulled by a rope
attached to a speed boat moving at a constant
velocity. Consider the following four forces
(1) the force of the boat pulling the rope, (2)
the force of the skier pulling on the rope, (3)
the force of the boat pushing the water, and (4)
the force of the water pushing on the boat.
Which two forces are an action-reaction pair
that is consistent with Newtons third law of
motion? a) 1 and 2 b) 2 and 3 c) 2 and
4 d) 3 and 4 e) 1 and 4
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4.5.1. A water skier is being pulled by a rope
attached to a speed boat moving at a constant
velocity. Consider the following four forces
(1) the force of the boat pulling the rope, (2)
the force of the skier pulling on the rope, (3)
the force of the boat pushing the water, and (4)
the force of the water pushing on the boat.
Which two forces are an action-reaction pair
that is consistent with Newtons third law of
motion? a) 1 and 2 b) 2 and 3 c) 2 and
4 d) 3 and 4 e) 1 and 4
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4.5.2. A large crate is lifted vertically at
constant speed by a rope attached to a
helicopter. Consider the following four forces
that arise in this situation (1) the weight of
the helicopter, (2) the weight of the crate, (3)
the force of the crate pulling on the earth, and
(4) the force of the helicopter pulling on the
rope. Which one of the following relationships
concerning the forces or their magnitudes is
correct? a) The magnitude of force 4 is greater
than that of force 2. b) The magnitude of force
4 is greater than that of force 1. c) Forces 3
and 4 are equal in magnitude, but oppositely
directed. d) Forces 2 and 4 are equal in
magnitude, but oppositely directed. e) The
magnitude of force 1 is less than that of force 2.
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4.5.2. A large crate is lifted vertically at
constant speed by a rope attached to a
helicopter. Consider the following four forces
that arise in this situation (1) the weight of
the helicopter, (2) the weight of the crate, (3)
the force of the crate pulling on the earth, and
(4) the force of the helicopter pulling on the
rope. Which one of the following relationships
concerning the forces or their magnitudes is
correct? a) The magnitude of force 4 is greater
than that of force 2. b) The magnitude of force
4 is greater than that of force 1. c) Forces 3
and 4 are equal in magnitude, but oppositely
directed. d) Forces 2 and 4 are equal in
magnitude, but oppositely directed. e) The
magnitude of force 1 is less than that of force 2.
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4.5.3. An astronaut is on a spacewalk outside her
ship in gravity-free space. Initially, the
spacecraft and astronaut are at rest with respect
to each other. Then, the astronaut pushes to the
left on the spacecraft and the astronaut
accelerates to the right. Which one of the
following statements concerning this situation is
true? a) The astronaut stops moving after she
stops pushing on the spacecraft. b) The
velocity of the astronaut increases while she is
pushing on the spacecraft. c) The force exerted
on the astronaut is larger than the force exerted
on the spacecraft. d) The spacecraft does not
move, but the astronaut moves to the right with a
constant speed. e) The force exerted on the
spacecraft is larger than the force exerted on
the astronaut.
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4.5.3. An astronaut is on a spacewalk outside her
ship in gravity-free space. Initially, the
spacecraft and astronaut are at rest with respect
to each other. Then, the astronaut pushes to the
left on the spacecraft and the astronaut
accelerates to the right. Which one of the
following statements concerning this situation is
true? a) The astronaut stops moving after she
stops pushing on the spacecraft. b) The
velocity of the astronaut increases while she is
pushing on the spacecraft. c) The force exerted
on the astronaut is larger than the force exerted
on the spacecraft. d) The spacecraft does not
move, but the astronaut moves to the right with a
constant speed. e) The force exerted on the
spacecraft is larger than the force exerted on
the astronaut.
26
4.7.1. A cannon fires a ball vertically upward
from the Earths surface. Which one of the
following statements concerning the net force
acting on the ball at the top of its trajectory
is correct? a) The net force on the ball is
instantaneously equal to zero newtons at the top
of the flight path. b) The direction of the net
force on the ball changes from upward to
downward. c) The net force on the ball is less
than the weight, but greater than zero
newtons. d) The net force on the ball is
greater than the weight of the ball. e) The net
force on the ball is equal to the weight of the
ball.
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4.7.1. A cannon fires a ball vertically upward
from the Earths surface. Which one of the
following statements concerning the net force
acting on the ball at the top of its trajectory
is correct? a) The net force on the ball is
instantaneously equal to zero newtons at the top
of the flight path. b) The direction of the net
force on the ball changes from upward to
downward. c) The net force on the ball is less
than the weight, but greater than zero
newtons. d) The net force on the ball is
greater than the weight of the ball. e) The net
force on the ball is equal to the weight of the
ball.
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4.7.2. If an object at the surface of the Earth
has a weight W, what would be the weight of the
object if it was transported to the surface of a
planet that is one-sixth the mass of Earth and
has a radius one third that of Earth? a) 3W b)
4W/3 c) W d) 3W/2 e) W/3
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4.7.2. If an object at the surface of the Earth
has a weight W, what would be the weight of the
object if it was transported to the surface of a
planet that is one-sixth the mass of Earth and
has a radius one third that of Earth? a) 3W b)
4W/3 c) W d) 3W/2 e) W/3
30
4.7.3. Two objects that may be considered point
masses are initially separated by a distance d.
The separation distance is then decreased to d/3.
How does the gravitational force between these
two objects change as a result of the
decrease? a) The force will not change since it
is only dependent on the masses of the
objects. b) The force will be nine times larger
than the initial value. c) The force will be
three times larger than the initial value. d)
The force will be one third of the initial
value. e) The force will be one ninth of the
initial value.
31
4.7.3. Two objects that may be considered point
masses are initially separated by a distance d.
The separation distance is then decreased to d/3.
How does the gravitational force between these
two objects change as a result of the
decrease? a) The force will not change since it
is only dependent on the masses of the
objects. b) The force will be nine times larger
than the initial value. c) The force will be
three times larger than the initial value. d)
The force will be one third of the initial
value. e) The force will be one ninth of the
initial value.
32
4.7.4. Two satellites of masses m and 2m are at
opposite sides of the same circular orbit about
the Earth. Which one of the following statements
is true? a) The magnitude of the gravitational
force is greater for the satellite of mass 2m
than it is for the other satellite. b) The
magnitude of the gravitational force is the same
for both satellites and it is greater than zero
newtons. c) Since the satellites are moving at
a constant velocity, the gravitational force on
the satellites must be zero newtons. d) The
magnitude of the gravitational force is greater
for the satellite of mass m than it is for the
other satellite. e) The satellite of mass 2m
must move faster in the orbit than the other and
eventually they will be on the same side of the
Earth.
33
4.7.4. Two satellites of masses m and 2m are at
opposite sides of the same circular orbit about
the Earth. Which one of the following statements
is true? a) The magnitude of the gravitational
force is greater for the satellite of mass 2m
than it is for the other satellite. b) The
magnitude of the gravitational force is the same
for both satellites and it is greater than zero
newtons. c) Since the satellites are moving at
a constant velocity, the gravitational force on
the satellites must be zero newtons. d) The
magnitude of the gravitational force is greater
for the satellite of mass m than it is for the
other satellite. e) The satellite of mass 2m
must move faster in the orbit than the other and
eventually they will be on the same side of the
Earth.
34
4.7.5. An astronaut, whose mass on the surface of
the Earth is m, orbits the Earth in the space
shuttle at an altitude of 450 km. What is her
mass while orbiting in the space shuttle? a)
0.125m b) 0.25m c) 0.50m d) 0.75m e) m
35
4.7.5. An astronaut, whose mass on the surface of
the Earth is m, orbits the Earth in the space
shuttle at an altitude of 450 km. What is her
mass while orbiting in the space shuttle? a)
0.125m b) 0.25m c) 0.50m d) 0.75m e) m
36
4.8.1. A free-body diagram is shown for the
following situation a force pulls on a crate of
mass m on a rough surface. The diagram shows the
magnitudes and directions of the forces that act
on the crate in this situation. represents
the normal force on the crate, represents the
acceleration due to gravity, and represents
the frictional force. Which one of the following
expressions is equal to the magnitude of the
normal force? a) P ? f / ? b) P ? f c) P ?
f ? mg d) mg e) zero
37
4.8.1. A free-body diagram is shown for the
following situation a force pulls on a crate of
mass m on a rough surface. The diagram shows the
magnitudes and directions of the forces that act
on the crate in this situation. represents
the normal force on the crate, represents the
acceleration due to gravity, and represents
the frictional force. Which one of the following
expressions is equal to the magnitude of the
normal force? a) P ? f / ? b) P ? f c) P ?
f ? mg d) mg e) zero
38
4.8.2. A free-body diagram is shown for the
following situation a force pulls on a crate
that is sitting on a rough surface. The force
is directed at an angle ? above the horizontal
direction. The diagram shows the magnitudes and
directions of the forces that act on the crate in
this situation. represents the normal force
on the crate, represents the weight of the
crate, and represents the frictional force.
Which one of the following actions would result
in an increase in the normal force? a) Decrease
the angle ?. b) Increase the magnitude of
. c) Decrease the coefficient of friction. d)
Decrease the magnitude of . e) Increase the
coefficient of friction
39
4.8.2. A free-body diagram is shown for the
following situation a force pulls on a crate
that is sitting on a rough surface. The force
is directed at an angle ? above the horizontal
direction. The diagram shows the magnitudes and
directions of the forces that act on the crate in
this situation. represents the normal force
on the crate, represents the weight of the
crate, and represents the frictional force.
Which one of the following actions would result
in an increase in the normal force? a) Decrease
the angle ?. b) Increase the magnitude of
. c) Decrease the coefficient of friction. d)
Decrease the magnitude of . e) Increase the
coefficient of friction
40
4.8.3. Consider the three cases shown in the
drawing in which the same force is applied to
a box of mass M. In which case(s) will the
magnitude of the normal force on the box equal (F
sin ? Mg)? a) Case One only b) Case Two
only c) Case Three only d) Cases One and Two
only e) Cases Two and Three only
41
4.8.3. Consider the three cases shown in the
drawing in which the same force is applied to
a box of mass M. In which case(s) will the
magnitude of the normal force on the box equal (F
sin ? Mg)? a) Case One only b) Case Two
only c) Case Three only d) Cases One and Two
only e) Cases Two and Three only
42
4.8.4. Consider the situation shown in the
drawing. Block A has a mass 1.0 kg and block B
has a mass 3.0 kg. The two blocks are connected
by a very light rope of negligible mass that
passes over a pulley as shown. The coefficient
of kinetic friction for the blocks on the ramp is
0.33. The ramp is angled at ? 45?. At time t
0 s, block A is released with an initial speed
of 6.0 m/s. What is the tension in the rope? a)
11.8 N b) 7.88 N c) 15.8 N d) 13.6 N e)
9.80 N
43
4.8.4. Consider the situation shown in the
drawing. Block A has a mass 1.0 kg and block B
has a mass 3.0 kg. The two blocks are connected
by a very light rope of negligible mass that
passes over a pulley as shown. The coefficient
of kinetic friction for the blocks on the ramp is
0.33. The ramp is angled at ? 45?. At time t
0 s, block A is released with an initial speed
of 6.0 m/s. What is the tension in the rope? a)
11.8 N b) 7.88 N c) 15.8 N d) 13.6 N e)
9.80 N
44
4.9.1. On a rainy evening, a truck is driving
along a straight, level road at 25 m/s. The
driver panics when a deer runs onto the road and
locks the wheels while braking. If the
coefficient of friction for the wheel/road
interface is 0.68, how far does the truck slide
before it stops? a) 55 m b) 47 m c) 41
m d) 36 m e) 32 m
45
4.9.1. On a rainy evening, a truck is driving
along a straight, level road at 25 m/s. The
driver panics when a deer runs onto the road and
locks the wheels while braking. If the
coefficient of friction for the wheel/road
interface is 0.68, how far does the truck slide
before it stops? a) 55 m b) 47 m c) 41
m d) 36 m e) 32 m
46
4.9.2. Jennifer is pushing a heavy box up a rough
inclined surface at a constant speed by applying
a horizontal force F as shown in the drawing.
The coefficient of kinetic friction for the box
on the inclined surface is ?k. Which one of the
following expressions correctly determines the
normal force on the box? a) b) c) d) e)
47
4.9.2. Jennifer is pushing a heavy box up a rough
inclined surface at a constant speed by applying
a horizontal force F as shown in the drawing.
The coefficient of kinetic friction for the box
on the inclined surface is ?k. Which one of the
following expressions correctly determines the
normal force on the box? a) b) c) d) e)
48
4.9.3. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
that there is no slipping of the top crate as a
horizontal force is applied to the bottom
crate, determine an expression for the static
frictional force acting on the top crate. a) f
F b) c) d) e)
49
4.9.3. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
that there is no slipping of the top crate as a
horizontal force is applied to the bottom
crate, determine an expression for the static
frictional force acting on the top crate. a) f
F b) c) d) e)
50
4.9.4. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
a horizontal force is applied to the bottom
crate, determine an expression for the minimum
static coefficient of friction so that the top
crate does not slip. a) b) c) d) e)
51
4.9.4. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
a horizontal force is applied to the bottom
crate, determine an expression for the minimum
static coefficient of friction so that the top
crate does not slip. a) b) c) d) e)
52
4.9.5. Three pine blocks, each with identical
mass, are sitting on a rough surface as shown.
If the same horizontal force is applied to each
block, which one of the following statements is
false? a) The coefficient of kinetic
friction is the same for all three blocks. b)
The magnitude of the force of kinetic friction is
greater for block 3. c) The normal force
exerted by the surface is the same for all three
blocks. d) Block 3 has the greatest apparent
area in contact with the surface. e) If the
horizontal force is the minimum to start block 1
moving, then that same force could be used to
start block 2 or block 3 moving.
53
4.9.5. Three pine blocks, each with identical
mass, are sitting on a rough surface as shown.
If the same horizontal force is applied to each
block, which one of the following statements is
false? a) The coefficient of kinetic
friction is the same for all three blocks. b)
The magnitude of the force of kinetic friction is
greater for block 3. c) The normal force
exerted by the surface is the same for all three
blocks. d) Block 3 has the greatest apparent
area in contact with the surface. e) If the
horizontal force is the minimum to start block 1
moving, then that same force could be used to
start block 2 or block 3 moving.
54
4.9.6. Jake bought a new dog and is carrying a
new dog house on the flatbed of his brand new
pickup truck. Jake isnt sure if he should tie
the house down, but he doesnt want it to scratch
the paint if it should slide during braking.
During the trip home, Jake will travel along
straight, level roads and have to stop from a
maximum speed of 21 m/s in a distance of 29 m.
What is the minimum coefficient of static
friction between the dog house and the paint that
is required to prevent it from sliding? Compare
your answer to the actual coefficient of friction
of 0.35 to determine if the dog house should be
tied down. a) 0.22, no need to tie the house
down b) 0.30, no need to tie the house down c)
0.35, he may want to tie it down just in
case d) 0.56, the house needs to be tied
down e) 0.78, the house needs to be tied down
55
4.9.6. Jake bought a new dog and is carrying a
new dog house on the flatbed of his brand new
pickup truck. Jake isnt sure if he should tie
the house down, but he doesnt want it to scratch
the paint if it should slide during braking.
During the trip home, Jake will travel along
straight, level roads and have to stop from a
maximum speed of 21 m/s in a distance of 29 m.
What is the minimum coefficient of static
friction between the dog house and the paint that
is required to prevent it from sliding? Compare
your answer to the actual coefficient of friction
of 0.35 to determine if the dog house should be
tied down. a) 0.22, no need to tie the house
down b) 0.30, no need to tie the house down c)
0.35, he may want to tie it down just in
case d) 0.56, the house needs to be tied
down e) 0.78, the house needs to be tied down
56
4.10.1. Some children are pulling on a rope that
is raising a bucket via a pulley up to their tree
house. The bucket containing their lunch is
rising at a constant velocity. Ignoring the mass
of the rope, but not ignoring air resistance,
which one of the following statements concerning
the tension in the rope is true? a) The
magnitude of the tension is zero newtons. b)
The direction of the tension is downward. c)
The magnitude of the tension is equal to that of
the weight of the bucket. d) The magnitude of
the tension is less than that of the weight of
the bucket. e) The magnitude of the tension is
greater than that of the weight of the bucket.
57
4.10.1. Some children are pulling on a rope that
is raising a bucket via a pulley up to their tree
house. The bucket containing their lunch is
rising at a constant velocity. Ignoring the mass
of the rope, but not ignoring air resistance,
which one of the following statements concerning
the tension in the rope is true? a) The
magnitude of the tension is zero newtons. b)
The direction of the tension is downward. c)
The magnitude of the tension is equal to that of
the weight of the bucket. d) The magnitude of
the tension is less than that of the weight of
the bucket. e) The magnitude of the tension is
greater than that of the weight of the bucket.
58
4.10.2. One end of a string is tied to a tree
branch at a height h above the ground. The other
end of the string, which has a length L h, is
tied to a rock. The rock is then dropped from
the branch. Which one of the following
statements concerning the tension in the string
is true as the rock falls? a) The tension is
independent of the magnitude of the rocks
acceleration. b) The magnitude of the tension
is equal to the weight of the rock. c) The
magnitude of the tension is less than the weight
of the rock. d) The magnitude of the tension is
greater than the weight of the rock. e) The
tension increases as the speed of the rock
increases as it falls.
59
4.10.2. One end of a string is tied to a tree
branch at a height h above the ground. The other
end of the string, which has a length L h, is
tied to a rock. The rock is then dropped from
the branch. Which one of the following
statements concerning the tension in the string
is true as the rock falls? a) The tension is
independent of the magnitude of the rocks
acceleration. b) The magnitude of the tension
is equal to the weight of the rock. c) The
magnitude of the tension is less than the weight
of the rock. d) The magnitude of the tension is
greater than the weight of the rock. e) The
tension increases as the speed of the rock
increases as it falls.
60
4.10.3. A rock is suspended from a string.
Barbara accelerates the rock upward with a
constant acceleration by pulling on the other end
of the string. Which one of the following
statements concerning the tension in the string
is true? a) The tension is independent of the
magnitude of the rocks acceleration. b) The
magnitude of the tension is equal to the weight
of the rock. c) The magnitude of the tension is
less than the weight of the rock. d) The
magnitude of the tension is greater than the
weight of the rock. e) The tension decreases as
the speed of the rock increases as it rises.
61
4.10.3. A rock is suspended from a string.
Barbara accelerates the rock upward with a
constant acceleration by pulling on the other end
of the string. Which one of the following
statements concerning the tension in the string
is true? a) The tension is independent of the
magnitude of the rocks acceleration. b) The
magnitude of the tension is equal to the weight
of the rock. c) The magnitude of the tension is
less than the weight of the rock. d) The
magnitude of the tension is greater than the
weight of the rock. e) The tension decreases as
the speed of the rock increases as it rises.
62
4.11.1. Consider the following (i) the book is
at rest, (ii) the book is moving at a constant
velocity, (iii) the book is moving with a
constant acceleration. Under which of these
conditions is the book in equilibrium? a) (i)
only b) (ii) only c) (iii) only d) (i) and
(ii) only e) (ii) and (iii) only
63
4.11.1. Consider the following (i) the book is
at rest, (ii) the book is moving at a constant
velocity, (iii) the book is moving with a
constant acceleration. Under which of these
conditions is the book in equilibrium? a) (i)
only b) (ii) only c) (iii) only d) (i) and
(ii) only e) (ii) and (iii) only
64
4.11.2. A block of mass M is hung by ropes as
shown. The system is in equilibrium. The point
O represents the knot, the junction of the three
ropes. Which of the following statements is true
concerning the magnitudes of the three forces in
equilibrium? a) F1 F2 F3 b) F1 F2
0.5F3 c) F1 F2 F3 d) F1 gt F3 e) F2 lt F3
65
4.11.2. A block of mass M is hung by ropes as
shown. The system is in equilibrium. The point
O represents the knot, the junction of the three
ropes. Which of the following statements is true
concerning the magnitudes of the three forces in
equilibrium? a) F1 F2 F3 b) F1 F2
0.5F3 c) F1 F2 F3 d) F1 gt F3 e) F2 lt F3
66
4.11.3. A team of dogs pulls a sled of mass 2m
with a force . A second sled of mass m is
attached by a rope and pulled behind the first
sled. The tension in the rope is . Assuming
frictional forces are too small to consider,
determine the ratio of the magnitudes of the
forces and , that is, P/T. a) 3 b)
2 c) 1 d) 0.5 e) 0.33
67
4.11.3. A team of dogs pulls a sled of mass 2m
with a force . A second sled of mass m is
attached by a rope and pulled behind the first
sled. The tension in the rope is . Assuming
frictional forces are too small to consider,
determine the ratio of the magnitudes of the
forces and , that is, P/T. a) 3 b)
2 c) 1 d) 0.5 e) 0.33
68
4.12.1. A man stands on a bathroom scale that
indicates his weight is W. The man is standing
on the scale inside an elevator when it is at
rest. What will the scale read when the elevator
is moving upward at a constant velocity v? a)
The scale will read a value that is slightly less
than W. b) The scale will read a value that is
slightly greater than W. c) The scale will read
the same value W. d) The scale will read a
value that is much greater than W. e) The scale
will read zero newtons.
69
4.12.1. A man stands on a bathroom scale that
indicates his weight is W. The man is standing
on the scale inside an elevator when it is at
rest. What will the scale read when the elevator
is moving upward at a constant velocity v? a)
The scale will read a value that is slightly less
than W. b) The scale will read a value that is
slightly greater than W. c) The scale will read
the same value W. d) The scale will read a
value that is much greater than W. e) The scale
will read zero newtons.
70
4.12.2. In a moving elevator, a woman standing on
a bathroom scale notices that the reading on the
scale is significantly larger than when the
elevator was at rest. The elevator itself only
has two forces acting on it the tension in a
cable and the force of gravity. Which one of the
following statements is false concerning this
situation? a) The elevator is uniformly
accelerating. b) The elevators speed is
increasing as it moves upward. c) The tension
in the cable exceeds the weight of the elevator
and its contents. d) The elevator could be
moving upward at constant speed. e) The
elevator could be moving downward with decreasing
speed.
71
4.12.2. In a moving elevator, a woman standing on
a bathroom scale notices that the reading on the
scale is significantly larger than when the
elevator was at rest. The elevator itself only
has two forces acting on it the tension in a
cable and the force of gravity. Which one of the
following statements is false concerning this
situation? a) The elevator is uniformly
accelerating. b) The elevators speed is
increasing as it moves upward. c) The tension
in the cable exceeds the weight of the elevator
and its contents. d) The elevator could be
moving upward at constant speed. e) The
elevator could be moving downward with decreasing
speed.
72
4.12.3. A block of mass m is pressed against a
wall with an initial force and the block is
at rest. The coefficient of static friction for
the block against the wall is equal to 0.5. The
coefficient of kinetic friction is less than the
coefficient of static friction. If the force
is equal to the weight of the block, which one of
the following statements is true? a) The block
will continue to remain at rest because the force
of static friction is two times the weight of the
block. b) The block will slide down the wall
because the force of static friction is only
equal to one-half of the blocks weight. c) The
block will accelerate at 9.8 m/s2 down the
wall. d) The block will slide down the wall at
constant speed. e) The block will accelerate at
less than 4.9 m/s2 down the wall.
73
4.12.3. A block of mass m is pressed against a
wall with an initial force and the block is
at rest. The coefficient of static friction for
the block against the wall is equal to 0.5. The
coefficient of kinetic friction is less than the
coefficient of static friction. If the force
is equal to the weight of the block, which one of
the following statements is true? a) The block
will continue to remain at rest because the force
of static friction is two times the weight of the
block. b) The block will slide down the wall
because the force of static friction is only
equal to one-half of the blocks weight. c) The
block will accelerate at 9.8 m/s2 down the
wall. d) The block will slide down the wall at
constant speed. e) The block will accelerate at
less than 4.9 m/s2 down the wall.
74
4.12.4. A force of magnitude F pushes a block of
mass 2m, which in turn pushes a block of mass m
as shown. The blocks are accelerated across a
horizontal, frictionless surface. What is the
magnitude of the force that the smaller block
exerts on the larger block? a) F/3 b)
F/2 c) F d) 2F e) 3F
75
4.12.4. A force of magnitude F pushes a block of
mass 2m, which in turn pushes a block of mass m
as shown. The blocks are accelerated across a
horizontal, frictionless surface. What is the
magnitude of the force that the smaller block
exerts on the larger block? a) F/3 b)
F/2 c) F d) 2F e) 3F
76
4.12.5. A box is held by a rope on a frictionless
inclined surface as shown. What will the
magnitude of the acceleration of the box be if
the rope breaks? a) g b) g sin ? c) g cos
? d) g tan ? e) zero m/s2
77
4.12.5. A box is held by a rope on a frictionless
inclined surface as shown. What will the
magnitude of the acceleration of the box be if
the rope breaks? a) g b) g sin ? c) g cos
? d) g tan ? e) zero m/s2
78
4.12.6. Two identical cement cylinders are
attached to the opposite ends of a spring scale
via very light ropes (the mass of which can be
neglected) that run over frictionless pulleys as
shown. When the same scale was suspended from
the ceiling and one of the cylinders was hung
from it, the scale indicated its weight is W
newtons. What will the scale read in the
configuration shown? a) zero newtons b) W/2
newtons c) W newtons d) 2W newtons e) 4W
newtons
79
4.12.6. Two identical cement cylinders are
attached to the opposite ends of a spring scale
via very light ropes (the mass of which can be
neglected) that run over frictionless pulleys as
shown. When the same scale was suspended from
the ceiling and one of the cylinders was hung
from it, the scale indicated its weight is W
newtons. What will the scale read in the
configuration shown? a) zero newtons b) W/2
newtons c) W newtons d) 2W newtons e) 4W
newtons