CH 8

D

A ruler is in equilibrium on the tip of your finger only if __________. A. the net torque is zero B. nobody touches the ruler C. the net force is zero D. net torque and net force are zero

C

As distance increases between most of the mass of an object and its center of rotation, how does rotational inertia change? A. It stays the same. B. It goes to zero. C. It increases. D. It decreases.

D

How can gravity be simulated in an orbiting space station? A. Rotate a cylinder to create centrifugal force as viewed by a person on the inside of the curved outer wall B. Spin a station shaped like a bicycle wheel C. Spin two pods connected by a cable D. All of the above

B

How do clockwise and counterclockwise torques compare when a system is balanced? A. The counterclockwise torque is greater. B. They are equal in magnitude and opposite in direction. C. The clockwise torque is greater. D. They are both zero.

C

How does the torque due to the weight of one side of the broom exerted around the balance point compare with the torque exerted by the weight of the other side of the broom around the balance point? A. The torque due to the weight of the shorter side (the bristles of the broom) is larger in magnitude than the torque due to the weight of the longer side (the handle), and opposite in direction. B. The torque due to the weight of the shorter side (the bristles of the broom) is smaller in magnitude than the torque due to the weight of the longer side, and opposite in direction. C. The torque due to the weight of the shorter side (the bristles of the broom) is equal in magnitude to the torque due to the weight of the longer side, and opposite in direction.

A

Rotational inertia of an object rotating about an axis becomes greater with _______. A. increased mass and increased distance to mass concentration B. decreased mass and decreased distance to mass concentration C. decreased mass D. increased mass

E

Suppose we replace the mass in the video with one that is four times heavier. How far from the free end must we place the pivot to keep the meter stick in balance? A. 50 cm (in the middle) B. 75 cm (25 cm from the weight) C. 10 cm D. 25 cm E. 90 cm (10 cm from the weight)

A

The center of gravity of a basketball is located _______. A. at its geometrical center B. at a point opposite to its center of mass C. at the point of application when balanced D. in the material making up its mass

C

The rotational speed of every point of a rotating rigid object _______. A. depends on the distance to the axis of rotation B. is tangent to the circular motion C. is the same D. is zero

C

The tangential speed on the outer edge of a rotating carousel is _______. A. the same as toward the center B. four times as great for twice the distance C. greater than toward the center D. less than toward the center

A

The torque exerted by a crowbar on an object increases with increased _______. A. force and leverage distance B. energy of application C. rotational inertia D. force

C

To double the rotational speed the centripetal force must _______. A. double B. increase C. be four times larger D. stay the same

A

To improve the performance of a racing bicycle, the mass of the tires and rims is reduced so there is ____________. A. less rotational inertia B. less air resistance C. less friction D. more rotational inertia

D

Why does bending your legs when running enable you to swing your legs to and fro more rapidly? A. Bending your legs decreases the angular speed, thus reducing rotational inertia. B. Bending your legs increases the height of the foot, thus reducing rotational inertia. C. Bending your legs puts the rotational axis in the center of the leg, thus reducing rotational inertia. D. Bending your legs shortens them, thus reducing rotational inertia.

B

How does the force needed to turn the wrench change if you increase the lever arm? A. It increases. B. It decreases. C. It stays the same.

B

How does the lever arm change if you decrease the angle of the force? A. It stays the same. B. It decreases. C. It increases.

A

How does the lever arm change when you decrease the distance to the nut? A. It decreases. B. It increases. C. It stays the same.

B

How does the rotational inertia of the rod with the mass toward the bottom compare with the rotational inertia of the mass toward the top? A. The rotational inertia of the rod with the mass closer to the bottom is greater than the rotational inertia of the rod with the mass closer to the top. B. The rotational inertia of the rod with the mass closer to the top is greater than the rotational inertia of the rod with the mass closer to the bottom. C. he rotational inertia of the rod with the mass closer to the top is equal to the rotational inertia of the rod with the mass closer to the bottom.

C

Is it easier for a circus performer to balance a long rod held vertically with people hanging off the other end, or the same long rod without the people at the other end, and why? A. It is easier for the performer to balance a long rod held vertically without people at the other end because the rotational inertia is greater. B. It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is smaller. C. It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is greater. D. It is easier for the performer to balance a long rod held vertically without people at the other end because the rotational inertia is smaller.

C

Is it easier to balance a long rod with a mass attached to it when the mass is closer to your hand or when the mass is farther away? A. It is equally easy in both cases. B. It is easier when the mass is closer to your hand. C. It is easier when the mass is farther from your hand.

B

What is meant by the "lever arm" of a torque? A. It is the distance between the point at which a force is applied and the rotational axis. B. It is the perpendicular distance from the rotational axis to the line along which the force acts. C. It is the angle between the applied force vector and the rotational axis. D. It is the distance between the point at which a force is applied and the center of mass of an object.

B

When Dr. Hewitt cuts the broom right through the center of gravity, how do the weights of the two sides of the broom compare? A. Both sides of the broom on either side of the center of gravity have equal weight. B. The shorter side, where the bristles of the broom are, has a greater weight than the handle. C. The longer side (the handle) has a greater weight than the bristle side.

D

When a rock tied to a string is whirled in a horizontal circle, doubling the speed _______. A. decreases the velocity B. doubles the velocity, but the string tension remains the same C. doubles the tension in the string D. quadruples the tension in the string

D

When a rock tied to a string whirled in a horizontal circle somehow doubles in mass but keeps the same speed, the string tension _______. A. decreases B. remains the same C. increases by four D. doubles

A

Where is the center of gravity of the broom that Dr. Hewitt holds up? A. at the balance point B. at the center of the broom C. at the center of the heavier side of the broom

B

Why does the rotational inertia of the rod with the attached mass closer to your hand compare the way it does with the rotational inertial of the rod with the attached mass farther away? A. Rotational inertia depends on whether the mass is lower or higher. Objects where the mass is higher have a greater rotational inertia. B. Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The farther the mass is, the higher the rotational inertia. C. Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The closer the mass is, the higher the rotational inertia.

C

Why doesn't the Leaning Tower of Pisa topple over? A. The center of gravity is at the center of the building. B. A vertical line through the center of gravity passes through the center of its support base. C. A vertical line through the center of gravity passes inside its support base. D. The center of gravity is suspended below its support base.

A

Why is centrifugal force in a rotating frame called a "fictitious force"? A. It is not a fundamental force of nature. Instead, it is a force that only appears in an accelerating frame of reference. B. An outside observer has to add in the centrifugal force to understand motion in a rotating frame of reference. C. It is a force physicists had to insert to make the equations work out right. D. Newton made it up.

A

Why it is easier to remove an old bolt if we add an extension to the wrench handle? A. Because a higher torque is applied B. Because the wrench is heavier C. Because a higher force is applied D. Because there is more mass