Question 1

A football thrown with a spinning motion is more stable than one thrown without spin because

Accepted Answer

A)  there is no net torque on a spinning object. 
B)  air flows more easily around spinning objects. 
C)  the torque generated by the spinning action is conserved. 
D)  the angular momentum of a spinning object can only be changed by applying a torque. 
A)  there is no net torque on a spinning object. 
B)  air flows more easily around spinning objects. 
C)  the torque generated by the spinning action is conserved. 
D)  the angular momentum of a spinning object can only be changed by applying a torque.

Question 2

If the net force on a body is zero the net torque _______________________ (is always, is not necessarily, cannot be) zero.

Accepted Answer

The answer of If the net force on a body...

Question 3

If a solid disk and a hoop are to have the same mass and rotational inertia, then the hoop must have a _________ radius.

Accepted Answer

The answer of If a solid disk and a hoop...

Question 4

In principle, a first-grader could measurably move the Earth if

Accepted Answer

A)  she pushed her hardest on the Earth. 
B)  she had a long enough lever. 
C)  she ran her fastest opposite the spin of the Earth. 
D)  she was at the North Pole and had a bicycle wheel spinning opposite the spin of Earth. 
A)  she pushed her hardest on the Earth. 
B)  she had a long enough lever. 
C)  she ran her fastest opposite the spin of the Earth. 
D)  she was at the North Pole and had a bicycle wheel spinning opposite the spin of Earth.

Question 5

Because the rotational inertia is higher, it is hardest in springboard diving to perform a forward somersault in

Accepted Answer

A)  the straight position (no bending at knees or waist). 
B)  the pike position (bending at the waist but not the knees). 
C)  the tuck position (bending at both the waist and knees). 
A)  the straight position (no bending at knees or waist). 
B)  the pike position (bending at the waist but not the knees). 
C)  the tuck position (bending at both the waist and knees).

Question 6

Holding out your hands sideways helps you keep your balance along a narrow set of stepping-stones because

Accepted Answer

A)  the arms outward balance your weight. 
B)  arms inward only add to your weight. 
C)  with arms outward, you've increased your total rotational inertia relative to the pivot point: your feet. 
D)  moving the arms outward puts a counter-torque on the stepping-stones.
Fill in the Blank Questions 
A)  the arms outward balance your weight. 
B)  arms inward only add to your weight. 
C)  with arms outward, you've increased your total rotational inertia relative to the pivot point: your feet. 
D)  moving the arms outward puts a counter-torque on the stepping-stones.
Fill in the Blank Questions

Question 7

If an object has an angular acceleration larger than zero, its angular __________ must be changing with time.

Accepted Answer

velocity o

Question 8

In using a long steel rod as a lever to move a large rock, where should the fulcrum be placed for a person to use the least amount of force to move the rock?

Accepted Answer

A)  Close to the person. 
B)  Exactly halfway between the person and the rock. 
C)  Anywhere in between; it makes no difference. 
D)  Close to the rock. 
A)  Close to the person. 
B)  Exactly halfway between the person and the rock. 
C)  Anywhere in between; it makes no difference. 
D)  Close to the rock.

Question 9

A top of rotational inertia 4.0 kg m2 receives a torque of 2.4 Nm from a physics professor. The angular acceleration of the body will be

Accepted Answer

A)  1.2 rev/s2. 
B)  6.0 rad/s2. 
C)  1.0 rad/s2. 
D)  6.0 rev/s2. 
E)  0.6 rad/s2. 
A)  1.2 rev/s2. 
B)  6.0 rad/s2. 
C)  1.0 rad/s2. 
D)  6.0 rev/s2. 
E)  0.6 rad/s2.

Question 10

The rotational inertia of an object depends on

Accepted Answer

A)  its color. 
B)  how fast it is spinning. 
C)  how its mass is distributed about the spin axis. 
D)  the amount of torque applied to it. 
E)  none of these. 
A)  its color. 
B)  how fast it is spinning. 
C)  how its mass is distributed about the spin axis. 
D)  the amount of torque applied to it. 
E)  none of these.

Question 11

When a planet moves closer to the Sun in an elliptical orbit, its rotational inertia

Accepted Answer

A)  does not change because the mass of the planet is constant. 
B)  gets smaller because its distance from the Sun is smaller. 
C)  gets smaller because the lever arm is shorter. 
D)  gets larger because the angular momentum must be conserved. 
E)  gets larger because the planet has more angular acceleration. 
A)  does not change because the mass of the planet is constant. 
B)  gets smaller because its distance from the Sun is smaller. 
C)  gets smaller because the lever arm is shorter. 
D)  gets larger because the angular momentum must be conserved. 
E)  gets larger because the planet has more angular acceleration.

Question 12

The rotational velocity of a 45 rev/min phonograph record in rad/s is approximately

Accepted Answer

A)  45 rad/s. 
B)  4.7 rad/s. 
C)  0.75 rad/s. 
D)  283 rad/s. 
E)  15.7 rad/s. 
A)  45 rad/s. 
B)  4.7 rad/s. 
C)  0.75 rad/s. 
D)  283 rad/s. 
E)  15.7 rad/s.

Question 13

A wheel is spinning on an axle. The linear velocity of a point on the rim is simply the product of the radius times the rotational velocity, as long as the rotational velocity is measured in units of

Accepted Answer

A)  deg/s. 
B)  rev/min. 
C)  rad/s. 
D)  rev/s. 
E)  deg/min. 
A)  deg/s. 
B)  rev/min. 
C)  rad/s. 
D)  rev/s. 
E)  deg/min.

Question 14

The stability of a bicycle is due to angular momentum of the wheels when the bicycle is moving forward. The stability is due to the net angular momentum vector, which

Accepted Answer

A)  points upward, perpendicular to the surface of Earth, thereby canceling the weight of the bicycle and rider. 
B)  points to the rider's left. 
C)  increases when the bicycle slows down due to conservation of energy. 
D)  is actually zero, since the back wheel cancels the angular momentum of the front wheel. 
A)  points upward, perpendicular to the surface of Earth, thereby canceling the weight of the bicycle and rider. 
B)  points to the rider's left. 
C)  increases when the bicycle slows down due to conservation of energy. 
D)  is actually zero, since the back wheel cancels the angular momentum of the front wheel.

Question 15

Even a little first-grader can stay up on a bicycle if he can get his bicycle moving fast enough because

Accepted Answer

A)  the angular momentum of the wheels wants to stay horizontal, due to conservation of angular momentum. 
B)  the first-grader's weight causes a torque too small to make the bicycle fall sideways when moving. 
C)  pedaling faster is easier once you are stable, and more pedaling increases net angular momentum. 
D)  All of these. 
A)  the angular momentum of the wheels wants to stay horizontal, due to conservation of angular momentum. 
B)  the first-grader's weight causes a torque too small to make the bicycle fall sideways when moving. 
C)  pedaling faster is easier once you are stable, and more pedaling increases net angular momentum. 
D)  All of these.

Question 16

The angular momentum of a rotating body is conserved when

Accepted Answer

A)  no net torque acts on the body. 
B)  no net force acts on the body. 
C)  when the body has a constant angular acceleration. 
D)  the shape of the body does not change. 
A)  no net torque acts on the body. 
B)  no net force acts on the body. 
C)  when the body has a constant angular acceleration. 
D)  the shape of the body does not change.

Question 17

A solid disk and a hoop have different diameters but identical masses. Which one has a larger rotational inertia?

Accepted Answer

A)  The solid disk. 
B)  The hoop. 
C)  It is impossible to know without knowing the diameters. 
D)  It is impossible to know without knowing the torques acting on the two objects. 
A)  The solid disk. 
B)  The hoop. 
C)  It is impossible to know without knowing the diameters. 
D)  It is impossible to know without knowing the torques acting on the two objects.

Question 18

The figure above shows two yo-yos that have the same mass and rotational inertia. The one on the right has a thicker axle than the one on the left. The torque produced by gravity is

Accepted Answer

A)  larger for the yo-yo on the right. 
B)  larger for the yo-yo on the left. 
C)  the same for both yo-yos. 
D)  zero; there is no net torque on the yo-yos. 
A)  larger for the yo-yo on the right. 
B)  larger for the yo-yo on the left. 
C)  the same for both yo-yos. 
D)  zero; there is no net torque on the yo-yos.

Question 19

An object is moving in a horizontal circle, in a clockwise direction (as viewed from above). In which direction does its angular momentum vector point?

Accepted Answer

A)  To the viewer's left 
B)  Away from the viewer 
C)  Toward the viewer 
D)  From the ball toward the center of the circle 
A)  To the viewer's left 
B)  Away from the viewer 
C)  Toward the viewer 
D)  From the ball toward the center of the circle

Question 20

Torque in the metric system is measured in units of

Accepted Answer

A)  N. 
B)  N s. 
C)  N rad. 
D)  N/m. 
E)  N m. 
A)  N. 
B)  N s. 
C)  N rad. 
D)  N/m. 
E)  N m.

Exam 8: Rotational Motion of Solid Objects

A football thrown with a spinning motion is more stable than one thrown without spin because

If the net force on a body is zero the net torque _______________________ (is always, is not necessarily, cannot be) zero.

If a solid disk and a hoop are to have the same mass and rotational inertia, then the hoop must have a _________ radius.

In principle, a first-grader could measurably move the Earth if

Because the rotational inertia is higher, it is hardest in springboard diving to perform a forward somersault in

Holding out your hands sideways helps you keep your balance along a narrow set of stepping-stones because

If an object has an angular acceleration larger than zero, its angular __________ must be changing with time.

In using a long steel rod as a lever to move a large rock, where should the fulcrum be placed for a person to use the least amount of force to move the rock?

A top of rotational inertia 4.0 kg m2 receives a torque of 2.4 Nm from a physics professor. The angular acceleration of the body will be

The rotational inertia of an object depends on

When a planet moves closer to the Sun in an elliptical orbit, its rotational inertia

The rotational velocity of a 45 rev/min phonograph record in rad/s is approximately

A wheel is spinning on an axle. The linear velocity of a point on the rim is simply the product of the radius times the rotational velocity, as long as the rotational velocity is measured in units of

The stability of a bicycle is due to angular momentum of the wheels when the bicycle is moving forward. The stability is due to the net angular momentum vector, which

Even a little first-grader can stay up on a bicycle if he can get his bicycle moving fast enough because

The angular momentum of a rotating body is conserved when

A solid disk and a hoop have different diameters but identical masses. Which one has a larger rotational inertia?

The figure above shows two yo-yos that have the same mass and rotational inertia. The one on the right has a thicker axle than the one on the left. The torque produced by gravity is

An object is moving in a horizontal circle, in a clockwise direction (as viewed from above). In which direction does its angular momentum vector point?

Torque in the metric system is measured in units of

Physics, the Fundamental Science

Describing Motion

Falling Objects and Projectile Motion

Newtons Laws: Explaining Motion

Circular Motion, the Planets, and Gravity

Energy and Oscillations

Momentum and Impulse

The Behavior of Fluids

Temperature and Heat

Heat Engines and the Second Law of Thermodynamics

Electrostatic Phenomena

Electric Circuits

Magnets and Electromagnetism

Making Waves

Light Waves and Color

Light and Image Formation

The Structure of the Atom

The Nucleus and Nuclear Energy

Relativity

Beyond Everyday Phenomena

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A top of rotational inertia 4.0 kg m² receives a torque of 2.4 Nm from a physics professor. The angular acceleration of the body will be