Rotational Motion Dynamics Conceptual

There must be equal amounts of mass on both sides of the center of mass (or center of gravity) of a system.

• True

• False

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 following are true statements? (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.

• Jacques and Ahmed have the same tangential speed.

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.

Five equal forces act on a rod that is free to pivot at point P, as shown in the figure. Which of these forces is producing a counter-clockwise torque about point P? (There could be more than one correct choice.)

• A

• B

• C

• D

• E

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 P due to this force the greatest?

• 1

• 2

• 3

• 4

• 5

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 a greater magnitude?

• the first force (at the midpoint)

• the second force (at the doorknob)

• The two forces are equal.

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° to the plane of the door.  Which force exerts the greater torque about the door hinge?

• the first force (applied perpendicular to the door)

• the second force (applied at an angle)

• Both forces exert equal non-zero torques.

• Both forces exert zero torque.

Five equal forces act on a rod that is free to pivot at point P, as shown in the figure. Which of these forces is producing a clockwise torque about point P? (There could be more than one correct choice.)

• A

• B

• C

• D

• E

If the sum of the external torques on an object is zero, then the sum of the external forces on it must also be zero.

• True

• False

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 P due to this force the least?

• 1

• 2

• 3

• 4

• 5