ROTATIONAL MOTION

How does the presence of L_⊥ affect the mechanical stress in a rotating shaft?

• It reduces stress
• It has no effect
• It causes vibrational stresses due to unbalanced angular momentum
• It cools the shaft

What is the relationship between the time derivative of L_z and external torque?

• They are unrelated
• dL_z/dt is half of τ_z
• dL_z/dt equals the external torque about the z-axis
• dL_z/dt is always zero

Why is the angular momentum vector not necessarily constant even if speed is constant in circular motion?

• Because mass changes
• Because ω decreases
• Because its direction depends on position, which changes continuously
• Because friction acts

What is the effect of increasing the radius of a rotating ring on its moment of inertia?

• It decreases linearly
• It remains unchanged
• It increases linearly
• It increases quadratically with radius

How does the angular momentum of a planet in elliptical orbit behave?

• It increases near perihelion
• It decreases near aphelion
• It remains constant in magnitude and direction
• It reverses direction