Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Cutnell/Johnson
Physics
Classroom Response System Questions
Chapter 4 Forces and Newton’s 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
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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 is falling 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 falls 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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4.2.3. A child is driving a bumper car at an amusement park. During one interval of the
ride, she is traveling at the car’s 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 net force acting on
them to hold them on her face during the collision.
b) During the collision, the girl’s 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 girl’s 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) 9
b) 3
c) 1
d) 1/3
e) 1/9
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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 car’s 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 > FB = FC
b) FC > FA > FB
c) FA < FB < FC
d) FA = FB = FC
e) FA = FC > 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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4.3.5. 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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4.3.6. During a baseball game, a boy lobs a ball from second base to first
base where it is caught by the first base player at the same height above
the ground from which it was tossed. The initial velocity of the ball is
directed at an angle of about 10° above the horizontal plane. Which one
of the following free-body diagrams best represents the forces applied to
the first baseman by the ball as it is caught?
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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 object’s acceleration while the force was being
applied
was dependent on the object’s initial velocity.
e) The change in the object’s 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 Newton’s 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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4.5.3. 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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4.7.1. A cannon fires a ball vertically upward from the Earth’s 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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4.7.3. 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.
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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 on the satellite of mass 2m
than it is on the other satellite.
b) The magnitude of the gravitational force is the same on 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 on the satellite of mass m than
it is on 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.
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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) greater than m
b) m
c) less than m
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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 horizontal 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 / µ
b) P - f
c) P - f - mg
d) mg
e) zero
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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 θ 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 θ.
b) Increase the magnitude of .
c) Decrease the coefficient of friction.
d) Decrease the magnitude of .
e) Increase the coefficient of friction
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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 θ + 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
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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 θ = 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) 12 N
b) 7.9 N
c) 16 N
d) 14 N
e) 5.9 N
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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
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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 µk. Which one of the
following expressions correctly determines the normal force on the box?
a)
b)
c)
d)
e)
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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)
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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)
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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.
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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 isn’t sure if he should tie the house down, but he
doesn’t 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
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4.9.7. Consider the three blocks shown in the drawing. The masses of
the blocks are given and there are frictional forces acting at the
interface between the blocks and the horizontal surface. A force is
applied on block 1 as shown but is too small to get the blocks
moving.
Complete the following statement: The net force acting on block 3 is
a) zero newtons
b) less than F but greater than 0
c) equal to F
d) greater than F
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4.9.8. Consider the three blocks shown in the drawing. The masses of
the blocks are given and there are frictional forces acting at the
interface between the blocks and the horizontal surface. A force is
applied on block 1 as shown. Complete the following statement:
The magnitude of the friction force acting on block 3 is
a) zero newtons
b) less than F
c) equal to F
d) greater than F
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4.9.9. A 1.0-kg block is placed against a wall and is held stationary by
a force of 8.0 N applied at a 45° angle as shown in the drawing.
What is the magnitude of the friction force?
a) 3.7 N
b) 4.1 N
c) 5.8 N
d) 7.0 N
e) 8.0 N
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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.
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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 depends on the magnitude of the rock’s 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.
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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 rock’s
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.
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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
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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. The angle theta is given to be 30o. Which of the
following statements is true concerning the magnitudes of the three
forces in equilibrium?
a) F1 + F2 = F3
b) F1 = F2 = 0.5×F3
c) F1 = F2 = F3
d) F1 > F3
e) F2 < F3
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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
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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.
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4.12.2. In a moving elevator, a woman standing on a bathroom scale notices
that the reading on the scale reading, while constant, 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 elevator’s 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.
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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 block’s 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.
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Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
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
sammonsa
Wednesday, October 7, 2015 9:02:45 AM Central Daylight Time
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Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
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 θ
c) g cos θ
d) g tan θ
e) zero m/s2
sammonsa
Wednesday, October 7, 2015 9:02:45 AM Central Daylight Time
70:cd:60:8a:0d:3a
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
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
sammonsa
Wednesday, October 7, 2015 9:02:45 AM Central Daylight Time
70:cd:60:8a:0d:3a