ROTATIONAL MOTION

If a rigid body is in mechanical equilibrium, which of the following must be true?

• Only net force is zero
• Only net torque is zero
• Both net force and net torque are zero
• The body must be at rest

What happens to the total angular momentum of a rigid body if an unbalanced torque acts on it?

• It remains constant
• It becomes zero instantly
• It changes with time
• It reverses every second

Why is the direction of angular momentum into the page in Fig. 6.19?

• Because the particle is moving downward
• Because gravity pulls it in
• Because the right-hand rule applied to r × v gives a vector pointing into the plane
• Because the angle is obtuse

In the context of a rigid body, what does translational equilibrium imply about the center of mass?

• It accelerates upward
• It rotates rapidly
• The center of mass moves with constant velocity or remains at rest
• It disappears

How does the conservation of angular momentum differ from linear momentum conservation?

• They are exactly the same
• Angular momentum depends on mass only
• Angular momentum conservation requires no net external torque, while linear momentum requires no net external force
• Linear momentum needs torque to be conserved