Physics Chapter 11

Which one of the following expressions allows one to calculate the angular momentum for a rigid body about a fixed axis?

I

Three objects, a solid sphere, a hollow ring, and a solid disk, have the same radius R. A string is wrapped around each object and the same tangential force is applied to each object at R and time t = 0 s. Which one of the following statements concerning the angular momentum of these objects after a short time t has elapsed, assuming the tangential force was continually applied?

The angular momentum of all of the objects has the same value.

A child standing on the edge of a freely spinning merry-go-round moves quickly to the center. Which one of the following statements is necessarily true concerning this event and why?

The angular speed of the system increases because the moment of inertia of the system has decreased.

Consider the following kinds of energy: (1) translational, (2) rotational, (3) elastic potential energy, and (4) gravitational potential energy. Which of these kinds of energy are involved when a wheel rolls without slipping along a flat, horizontal surface?

1 and 2 only

A wheel is rolling without slipping along a straight, level road. Which one of the following statements concerning the speed of the center of the wheel is true?

A point on the rim is moving at a tangential speed that is equal to the speed at the center of the wheel.

What happens when a spinning ice skater draws in her outstretched arms?

Her moment of inertia decreases causing her to speed up.

A solid cylinder is freely rolling down an inclined plane. What is the direction of the friction force acting on the cylinder and at what point does the friction force act?

The friction force acts at the point of contact between the cylinder and the plane and is directed up the plane.

Consider a system of particles. Which one of the following statements concerning the choice of the origin for this system is true?

The origin must be at the center of mass of the system of particles if the center of mass is accelerating.

Cylinders A and B are identical. Cylinder A is allowed to roll down a ramp without slipping. Cylinder B is allowed to slide down a similar ramp that has the same incline angle, but it is frictionless. Which one of the following statements concerning this situation, assuming the cylinders begin from rest at the same height, is true?

The sum of the translational and rotational kinetic energies of cylinder A is equal to the translational kinetic energy of cylinder B.

An object is rolling, so its motion involves both rotation and translation. Which one of the following statements must be true concerning this situation?

The total mechanical energy is equal to the sum of the translational and rotational kinetic energies and the gravitational potential energy of the object.

A solid cylinder is rolling along a flat, horizontal plane. The center of mass of the cylinder is moving toward the south at constant velocity. Which one of the following statements concerning the translational and rotational kinetic energies of the cylinder is true?

The translational kinetic energy is greater than the rotational kinetic energy

At the post office, a customer has dropped a coin. The coin is rolling on its side across the floor. Which one of the following statements concerning this situation is true?

There is no slipping at the point where the coin touches the floor.

The entrance door to a video store is pivoted about the hinges on the left side of the door. When you begin to push on the right side of the door to enter the store, what is the direction of the torque on the door?

Upward

The vector sum of all of the torques acting on a particle is equal to the time rate of change of which on of the following quantities?

angular momentum

There is a restaurant on top of a tall, circular building that is designed to rotate about its center at a constant angular speed. Which one of the following quantities is non-zero and constant for one of the restaurant's customers seated near a window?

angular momentum

At the carnival, a child is riding on a carousel. She has chosen to ride one of the animals near the outer rim, a Siberian tiger, even though it does move up and down. As the carousel is turning her bracelet falls from her wrist, even though her hand was firmly gripping a handle near the tiger's ear. Which of the following quantities for the bracelet is conserved as it falls?

angular momentum and mechanical energy

The wheels of a NASCAR racer roll without slipping as the car moves in a circular path at constant speed. Which one of the following quantities has a non-zero value and has a constant value in this situation?

angular velocity

SI Units for angular momentum

kg m2/s

A hoop rolls without slipping on a horizontal surface and it moves due east at a constant linear speed. What is the direction of its angular momentum?

north