Rotational Motion

When a rigid object rotates about a fixed axis, what is true about all the points in the object? (There could be more than one correct choice."

• They all have the same angular speed

• They all have the same tangential speed

• They all have the same angular acceleration

• They all have the same tangential acceleration

Two children, Ahmed and Jacques, ride on a merry-go-round. Ahmed is at a greater distance from the axis of rotation than Jacques. Which of the follow are true? (There could be more than one correct choice)

• Jacques has a greater angular speed than Ahmed

• Jacques and Ahmed have the same angular speed

• Jacques has a smaller angular speed than Ahmed

• Ahmed has a greater tangential speed than Jacques

Consider a uniform loop of radius R and mass M rolling without slipping. Which is larger, its translational kinetic energy or its rotational kinetic energy?

• Translational kinetic energy is larger

• Rotational kinetic energy is larger

• Both are equal

• You need to know the speed of the hoop to tell.

Consider a solid uniform sphere of radius R and mass M rolling without slipping. Which is larger, its translational kinetic energy or its rotational kinetic energy?

• Translational kinetic energy is larger

• Rotational kinetic energy is larger

• Both are equal

• You need to know the speed of the hoop to tell.

Two equal-magnitude forces are applied to a door at the doorknob. The first force is applied perpendicular to the door, and the second force is applied at 30 degrees to the plane of the door. Which force exerts the greater torque about the door hinge?

• the first force (perpendicular to the door)

• the second force (applied at the angle)

• Both forces exert equal non-zero torques

• Both forces exert zero torque

Two forces produce equal torques on a door about the door hinge. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force has the greater magnitude?

• the first force (at the midpoint)

• the second force (at the doorknob)

• the two forces are equal

A person sits on a freely spinning lab stool that has no friction in its axle. When this person extends her arms,

• her moment of inertia decreases and her angular speed increases

• her moment of inertia decreases and her angular speed decreases

• her moment of inertia increases and her angular speed increases

• her moment of inertia increases and her angular speed decreases

The figure shows scale drawings of four objects, each of the same mass and uniform thickness, with the mass distributed uniformly. Which one has the greatest moment of inertia when rotated about an axis perpendicular to the plane of the drawing at point p?

• A

• B

• C

• D

• The moment of inertia is the same for all of these objects.

A uniform ball is released from rest on a no-slip surface, as shown in the figure. After reaching its lowest point, the ball begins to rise again, this time on a frictionless surface. When the ball reaches its maximum height on the frictionless surface, it is

• higher than when it was released

• lower than when it was released

• at the same height from which it was released

• it is impossible to tell without knowing the mass of the ball

• it is impossible to tell without knowing the radius of the ball

As shown in the figure, a given force is applied to a rod in several different ways. In which case is the torque about the pivot point P due to this force the greatest?

• 1

• 2

• 3

• 4

• 5