Physics Quiz 10

Consider two uniform solid spheres where both have the same diameter, but one has twice the mass of the other. The ratio of the larger moment of inertia to that of the smaller moment of inertia is

2

Consider two equal mass cylinders rolling with the same translational velocity. The first cylinder (radius = R) is hollow and has a moment of inertia about its rotational axis of M R2, while the second cylinder (radius = r) is solid and has a moment of inertia about its axis of 0.5 M r2. What is the ratio of the hollow cylinder's angular momentum to that of the solid cylinder?

2R to r

Consider a rigid body that is rotating. Which of the following is an accurate statement?

All points on the body are moving with the same angular velocity

An object in motion with constant speed along a straight line can never have nonzero angular momentum.

False

If an object is in unstable equilibrium, any small displacement results in a restoring force or torque, which tends to return the object to its original equilibrium position.

False

When a rigid body rotates about a fixed axis all the points in the body have the same linear displacement.

False

A boy and a girl are riding on a merry-go-round that is turning. The boy is twice as far as the girl from the merry-go-round's center. If the boy and girl are of equal mass, which statement is true about the boy's moment of inertia with respect to the axis of rotation?

His moment of inertia is 4 times the girl's

An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his moment of inertia about the axis of rotation?

It decreases

An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his angular momentum about the axis of rotation?

It does not change

An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his rotational kinetic energy about the axis of rotation?

It increases

A planet of constant mass orbits the sun in an elliptical orbit. Neglecting any friction effects, what happens to the planet's rotational kinetic energy about the sun's center?

It increases when the planet approaches the sun, and decreases when it moves farther away.

A solid cylinder and a hollow cylinder have the same mass and the same radius. Which statement is true concerning their moment of inertia about an axis through the exact center of the flat surfaces?

The hollow cylinder has the greater moment of inertia

Unbalanced torques produce rotational accelerations, and balanced torques produce rotational equilibrium.

True

When a rigid body rotates about a fixed axis all the points in the body have the same angular speed.

True

The condition for rolling without slipping is that the center of mass speed is

Vcm = r ω

Consider a solid object which is subjected to a net torque. That object will experience which of the following?

an angular acceleration

A ball, solid cylinder, and a hollow pipe all have equal masses and radii. If the three are released simultaneously at the top of an inclined plane, which will reach the bottom first?

ball

A planet speeds up in its orbit as it gets closer to the sun because of

conservation of angular momentum

We can best understand how a diver is able to control his rate of rotation while in the air (and thus enter the water in a vertical position) by observing that while in the air

his angular momentum is constant

A pencil balanced on its tip such that it does not move

is in unstable equilibrium

A ball is attached to a string and revolves in a horizontal circle with angular momentum. When the string breaks at point B on the circumference, the ball moves off tangentially along path B-Q. As it moves along B-Q, increasing its distance from the center of the circle, its angular momentum

remains constant

If a constant net torque is applied to an object, that object will

rotate with constant angular acceleration

Angular momentum cannot be conserved if

there is net torque on the system

What condition or conditions is/are necessary for rotational equilibrium?

Στ = 0