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Cutnell/Johnson
Physics 7th edition
Classroom Response System Questions
Chapter 5 Dynamics of Uniform Circular Motion
Interactive Lecture Questions
5.1.1. An airplane flying at 115 m/s due east makes a gradual turn
while maintaining its speed and follows a circular path to fly
south. The turn takes 15 seconds to complete. What is the radius
of the circular path?
a) 410 m
b) 830 m
c) 1100 m
d) 1600 m
e) 2200 m
5.1.1. An airplane flying at 115 m/s due east makes a gradual turn
while maintaining its speed and follows a circular path to fly
south. The turn takes 15 seconds to complete. What is the radius
of the circular path?
a) 410 m
b) 830 m
c) 1100 m
d) 1600 m
e) 2200 m
5.2.1. A ball is whirled on the end of a string in a horizontal circle of
radius R at constant speed v. By which one of the following means
can the centripetal acceleration of the ball be increased by a factor
of two?
a) Keep the radius fixed and increase the period by a factor of two.
b) Keep the radius fixed and decrease the period by a factor of two.
c) Keep the speed fixed and increase the radius by a factor of two.
d) Keep the speed fixed and decrease the radius by a factor of two.
e) Keep the radius fixed and increase the speed by a factor of two.
5.2.1. A ball is whirled on the end of a string in a horizontal circle of
radius R at constant speed v. By which one of the following means
can the centripetal acceleration of the ball be increased by a factor
of two?
a) Keep the radius fixed and increase the period by a factor of two.
b) Keep the radius fixed and decrease the period by a factor of two.
c) Keep the speed fixed and increase the radius by a factor of two.
d) Keep the speed fixed and decrease the radius by a factor of two.
e) Keep the radius fixed and increase the speed by a factor of two.
5.2.2. A steel ball is whirled on the end of a chain in a horizontal circle
of radius R with a constant period T. If the radius of the circle is
then reduced to 0.75R, while the period remains T, what happens
to the centripetal acceleration of the ball?
a) The centripetal acceleration increases to 1.33 times its initial value.
b) The centripetal acceleration increases to 1.78 times its initial value.
c) The centripetal acceleration decreases to 0.75 times its initial value.
d) The centripetal acceleration decreases to 0.56 times its initial value.
e) The centripetal acceleration does not change.
5.2.2. A steel ball is whirled on the end of a chain in a horizontal circle
of radius R with a constant period T. If the radius of the circle is
then reduced to 0.75R, while the period remains T, what happens
to the centripetal acceleration of the ball?
a) The centripetal acceleration increases to 1.33 times its initial value.
b) The centripetal acceleration increases to 1.78 times its initial value.
c) The centripetal acceleration decreases to 0.75 times its initial value.
d) The centripetal acceleration decreases to 0.56 times its initial value.
e) The centripetal acceleration does not change.
5.2.3. While we are in this classroom, the Earth is orbiting the Sun in
an orbit that is nearly circular with an average radius of 1.50 × 1011
m. Assuming that the Earth is in uniform circular motion, what is
the centripetal acceleration of the Earth in its orbit around the Sun?
a) 5.9 × 103 m/s2
b) 1.9 × 105 m/s2
c) 3.2 × 107 m/s2
d) 7.0 × 102 m/s2
e) 9.8 m/s2
5.2.3. While we are in this classroom, the Earth is orbiting the Sun in
an orbit that is nearly circular with an average radius of 1.50 × 1011
m. Assuming that the Earth is in uniform circular motion, what is
the centripetal acceleration of the Earth in its orbit around the Sun?
a) 5.9 × 103 m/s2
b) 1.9 × 105 m/s2
c) 3.2 × 107 m/s2
d) 7.0 × 102 m/s2
e) 9.8 m/s2
5.3.1. A boy is whirling a stone at the end of a string around his head. The
string makes one complete revolution every second, and the tension in
the string is FT. The boy increases the speed of the stone, keeping the
radius of the circle unchanged, so that the string makes two complete
revolutions per second. What happens to the tension in the sting?
a) The tension increases to four times its original value.
b) The tension increases to twice its original value.
c) The tension is unchanged.
d) The tension is reduced to one half of its original value.
e) The tension is reduced to one fourth of its original value.
5.3.1. A boy is whirling a stone at the end of a string around his head. The
string makes one complete revolution every second, and the tension in
the string is FT. The boy increases the speed of the stone, keeping the
radius of the circle unchanged, so that the string makes two complete
revolutions per second. What happens to the tension in the sting?
a) The tension increases to four times its original value.
b) The tension increases to twice its original value.
c) The tension is unchanged.
d) The tension is reduced to one half of its original value.
e) The tension is reduced to one fourth of its original value.
5.3.2. An aluminum rod is designed to break when it is under a tension of
600 N. One end of the rod is connected to a motor and a 12-kg spherical
object is attached to the other end. When the motor is turned on, the
object moves in a horizontal circle with a radius of 6.0 m. If the speed of
the motor is continuously increased, at what speed will the rod break?
Ignore the mass of the rod for this calculation.
a) 11 m/s
b) 17 m/s
c) 34 m/s
d) 88 m/s
e) 3.0 × 102 m/s
5.3.2. An aluminum rod is designed to break when it is under a tension of
600 N. One end of the rod is connected to a motor and a 12-kg spherical
object is attached to the other end. When the motor is turned on, the
object moves in a horizontal circle with a radius of 6.0 m. If the speed of
the motor is continuously increased, at what speed will the rod break?
Ignore the mass of the rod for this calculation.
a) 11 m/s
b) 17 m/s
c) 34 m/s
d) 88 m/s
e) 3.0 × 102 m/s
5.3.3. A ball is attached to a string and whirled in a horizontal circle. The ball is
moving in uniform circular motion when the string separates from the ball (the
knot wasn’t very tight). Which one of the following statements best describes
the subsequent motion of the ball?
a) The ball immediately flies in the direction radially outward from the center of the
circular path the ball had been following.
b) The ball continues to follow the circular path for a short time, but then it
gradually falls away.
c) The ball gradually curves away from the circular path it had been following.
d) The ball immediately follows a linear path away from, but not tangent to the
circular path it had been following.
e) The ball immediately follows a line that is tangent to the circular path the ball had
been following
5.3.3. A ball is attached to a string and whirled in a horizontal circle. The ball is
moving in uniform circular motion when the string separates from the ball (the
knot wasn’t very tight). Which one of the following statements best describes
the subsequent motion of the ball?
a) The ball immediately flies in the direction radially outward from the center of the
circular path the ball had been following.
b) The ball continues to follow the circular path for a short time, but then it
gradually falls away.
c) The ball gradually curves away from the circular path it had been following.
d) The ball immediately follows a linear path away from, but not tangent to the
circular path it had been following.
e) The ball immediately follows a line that is tangent to the circular path the ball had
been following
5.3.4. A rancher puts a hay bail into the back of her SUV. Later, she
drives around an unbanked curve with a radius of 48 m at a speed of
16 m/s. What is the minimum coefficient of static friction for the hay
bail on the floor of the SUV so that the hay bail does not slide while
on the curve?
a) This cannot be determined without knowing the mass of the hay bail.
b) 0.17
c) 0.33
d) 0.42
e) 0.54
5.3.4. A rancher puts a hay bail into the back of her SUV. Later, she
drives around an unbanked curve with a radius of 48 m at a speed of
16 m/s. What is the minimum coefficient of static friction for the hay
bail on the floor of the SUV so that the hay bail does not slide while
on the curve?
a) This cannot be determined without knowing the mass of the hay bail.
b) 0.17
c) 0.33
d) 0.42
e) 0.54
5.4.1. The maximum speed at which a car can safely negotiate an
unbanked curve depends on all of the following factors except
a) the coefficient of kinetic friction between the road and the tires.
b) the coefficient of static friction between the road and the tires.
c) the acceleration due to gravity.
d) the diameter of the curve.
e) the ratio of the static frictional force between the road and the tires
and the normal force exerted on the car.
5.4.1. The maximum speed at which a car can safely negotiate an
unbanked curve depends on all of the following factors except
a) the coefficient of kinetic friction between the road and the tires.
b) the coefficient of static friction between the road and the tires.
c) the acceleration due to gravity.
d) the diameter of the curve.
e) the ratio of the static frictional force between the road and the tires
and the normal force exerted on the car.
5.4.2. A 1000-kg car travels along a straight portion of highway at a constant
velocity of 10 m/s, due east. The car then encounters an unbanked curve
of radius 50 m. The car follows the curve traveling at a constant speed
of 10 m/s while the direction of the car changes from east to south.
What is the magnitude of the acceleration of the car as it travels the
unbanked curve?
a) zero m/s2
b) 2 m/s2
c) 5 m/s2
d) 10 m/s2
e) 20 m/s2
5.4.2. A 1000-kg car travels along a straight portion of highway at a constant
velocity of 10 m/s, due east. The car then encounters an unbanked curve
of radius 50 m. The car follows the curve traveling at a constant speed
of 10 m/s while the direction of the car changes from east to south.
What is the magnitude of the acceleration of the car as it travels the
unbanked curve?
a) zero m/s2
b) 2 m/s2
c) 5 m/s2
d) 10 m/s2
e) 20 m/s2
5.4.3. You are riding in the forward passenger seat of a car as it travels
along a straight portion of highway. The car continues traveling at a
constant speed as it follows a sharp, unbanked curve to the left. You
feel the door pushing on the right side of your body. Which of the
following forces in the horizontal direction are acting on you?
a) a static frictional force between you and the seat
b) a normal force of the door
c) a force pushing you toward the door
d) answers a and b
e) answers a and c
5.4.3. You are riding in the forward passenger seat of a car as it travels
along a straight portion of highway. The car continues traveling at a
constant speed as it follows a sharp, unbanked curve to the left. You
feel the door pushing on the right side of your body. Which of the
following forces in the horizontal direction are acting on you?
a) a static frictional force between you and the seat
b) a normal force of the door
c) a force pushing you toward the door
d) answers a and b
e) answers a and c
5.4.4. A 1000-kg car travels along a straight portion of highway at a constant
velocity of 10 m/s, due east. The car then encounters an unbanked curve
of radius 50 m. The car follows the curve traveling at a constant speed
of 10 m/s while the direction of the car changes from east to south.
What is the magnitude of the frictional force between the tires and the
road as the car negotiates the unbanked curve?
a) 500 N
b) 1000 N
c) 2000 N
d) 5000 N
e) 10 000 N
5.4.4. A 1000-kg car travels along a straight portion of highway at a constant
velocity of 10 m/s, due east. The car then encounters an unbanked curve
of radius 50 m. The car follows the curve traveling at a constant speed
of 10 m/s while the direction of the car changes from east to south.
What is the magnitude of the frictional force between the tires and the
road as the car negotiates the unbanked curve?
a) 500 N
b) 1000 N
c) 2000 N
d) 5000 N
e) 10 000 N
5.5.1. A satellite is in a circular orbit around the Earth. If it is at an
altitude equal to twice the radius of the Earth, 2RE, how does its
speed v relate to the Earth's radius RE, and the magnitude g of the
acceleration due to gravity on the Earth's surface?
a) v  1
3
gRE
b) v  1
gRE
2
c) v 
2 gRE
d) v 
1 gR
E
2
1 gR
E
3
e) v 
5.5.1. A satellite is in a circular orbit around the Earth. If it is at an
altitude equal to twice the radius of the Earth, 2RE, how does its
speed v relate to the Earth's radius RE, and the magnitude g of the
acceleration due to gravity on the Earth's surface?
a) v  1
3
gRE
b) v  1
gRE
2
c) v 
2 gRE
d) v 
1 gR
E
2
1 gR
E
3
e) v 
5.5.2. It is the year 2094; and people are designing a new space station
that will be placed in a circular orbit around the Sun. The orbital
period of the station will be 6.0 years. Determine the ratio of the
station’s orbital radius about the Sun to that of the Earth’s orbital
radius about the Sun. Assume that the Earth’s obit about the Sun is
circular.
a) 2.4
b) 3.3
c) 4.0
d) 5.2
e) 6.0
5.5.2. It is the year 2094; and people are designing a new space station
that will be placed in a circular orbit around the Sun. The orbital
period of the station will be 6.0 years. Determine the ratio of the
station’s orbital radius about the Sun to that of the Earth’s orbital
radius about the Sun. Assume that the Earth’s obit about the Sun is
circular.
a) 2.4
b) 3.3
c) 4.0
d) 5.2
e) 6.0
5.5.3. A space probe is orbiting a planet on a circular orbit of radius R
and a speed v. The acceleration of the probe is a. Suppose rockets
on the probe are fired causing the probe to move to another
circular orbit of radius 0.5R and speed 2v. What is the magnitude
of the probe’s acceleration in the new orbit?
a) a/2
b) a
c) 2a
d) 4a
e) 8a
5.5.3. A space probe is orbiting a planet on a circular orbit of radius R
and a speed v. The acceleration of the probe is a. Suppose rockets
on the probe are fired causing the probe to move to another
circular orbit of radius 0.5R and speed 2v. What is the magnitude
of the probe’s acceleration in the new orbit?
a) a/2
b) a
c) 2a
d) 4a
e) 8a
5.6.1. A space station is designed in the shape of a large, hollow donut
that is uniformly rotating. The outer radius of the station is 460 m.
With what period must the station rotate so that a person sitting on
the outer wall experiences “artificial gravity,” i.e. an acceleration
of 9.8 m/s2?
a) 43 s
b) 76 s
c) 88 s
d) 110 s
e) 230 s
5.6.1. A space station is designed in the shape of a large, hollow donut
that is uniformly rotating. The outer radius of the station is 460 m.
With what period must the station rotate so that a person sitting on
the outer wall experiences “artificial gravity,” i.e. an acceleration
of 9.8 m/s2?
a) 43 s
b) 76 s
c) 88 s
d) 110 s
e) 230 s
5.7.1. At a circus, a clown on a motorcycle with a mass M travels along a
horizontal track and enters a vertical circle of radius r. Which one of
the following expressions determines the minimum speed that the
motorcycle must have at the top of the track to remain in contact with
the track?
a) v 
2 gr
b) v 
gr
c) v = gR
d) v = 2gR
e) v = MgR
5.7.1. At a circus, a clown on a motorcycle with a mass M travels along a
horizontal track and enters a vertical circle of radius r. Which one of
the following expressions determines the minimum speed that the
motorcycle must have at the top of the track to remain in contact with
the track?
a) v 
2 gr
b) v 
gr
c) v = gR
d) v = 2gR
e) v = MgR
5.7.2. A ball on the end of a rope is moving in a vertical circle near the
surface of the earth. Point A is at the top of the circle; C is at the
bottom. Points B and D are exactly halfway between A and C.
Which one of the following statements concerning the tension in
the rope is true?
a) The tension is smallest at point A.
b) The tension is smallest at point C.
c) The tension is smallest at both points B and D.
d) The tension is the same at points A and C.
e) The tension is the same at all four points.
5.7.2. A ball on the end of a rope is moving in a vertical circle near the
surface of the earth. Point A is at the top of the circle; C is at the
bottom. Points B and D are exactly halfway between A and C.
Which one of the following statements concerning the tension in
the rope is true?
a) The tension is smallest at point A.
b) The tension is smallest at point C.
c) The tension is smallest at both points B and D.
d) The tension is the same at points A and C.
e) The tension is the same at all four points.
5.7.3. An aluminum rod is designed to break when it is under a tension of 650 N.
One end of the rod is connected to a motor and a 12-kg spherical object is
attached to the other end. When the motor is turned on, the object moves in
a vertical circle with a radius of 6.0 m. If the speed of the motor is
continuously increased, what is the maximum speed the object can have at
the bottom of the circle without breaking the rod? Ignore the mass of the
rod for this calculation.
a) 4.0 m/s
b) 11 m/s
c) 16 m/s
d) 128 m/s
e) 266 m/s
5.7.3. An aluminum rod is designed to break when it is under a tension of 650 N.
One end of the rod is connected to a motor and a 12-kg spherical object is
attached to the other end. When the motor is turned on, the object moves in
a vertical circle with a radius of 6.0 m. If the speed of the motor is
continuously increased, what is the maximum speed the object can have at
the bottom of the circle without breaking the rod? Ignore the mass of the
rod for this calculation.
a) 4.0 m/s
b) 11 m/s
c) 16 m/s
d) 128 m/s
e) 266 m/s
5.7.4. A girl is swinging on a swing in the park. As she wings back and
forth, she follows a path that is part of a vertical circle. Her speed is
maximum at the lowest point on the circle and temporarily zero m/s at
the two highest points of the motion as her direction changes. Which of
the following forces act on the girl when she is at the lowest point on the
circle?
a) the force of gravity, which is directed downward
b) the force which is directed radially outward from the center of the circle
c) the tension in the chains of the swing, which is directed upward
d) answers b and c only
e) answers a and c only
5.7.4. A girl is swinging on a swing in the park. As she wings back and
forth, she follows a path that is part of a vertical circle. Her speed is
maximum at the lowest point on the circle and temporarily zero m/s at
the two highest points of the motion as her direction changes. Which of
the following forces act on the girl when she is at the lowest point on the
circle?
a) the force of gravity, which is directed downward
b) the force which is directed radially outward from the center of the circle
c) the tension in the chains of the swing, which is directed upward
d) answers b and c only
e) answers a and c only