Rotational Motion – Stage 2 (Page 2)

Very Short Answer & Reasoning Questions

These questions test concept clarity. Answers must be short, precise, and logical.

Q1. Why is torque zero when force passes through the axis?

Because the perpendicular distance (moment arm) from the axis is zero, hence torque τ = rF sinθ becomes zero.

Q2. Can a body rotate without having angular momentum?

No. Any rotating body must possess angular momentum. Angular momentum is a direct consequence of rotational motion.

Q3. Why does a hollow cylinder roll slower than a solid cylinder?

A hollow cylinder has a larger moment of inertia. Hence its acceleration is smaller while rolling.

Q4. Why is moment of inertia called rotational mass?

Because it resists angular acceleration in the same way mass resists linear acceleration.

Q5. Why does a skater rotate faster when arms are folded?

Folding arms decreases moment of inertia. To conserve angular momentum, angular velocity increases.

Q6. Why is friction necessary for rolling?

Friction provides the torque required for rotation. Without friction, the body would slide instead of rolling.

Q7. Why does moment of inertia depend on axis of rotation?

Because the distance of mass elements from the axis changes with axis, altering I = Σmr².

Q8. Is angular momentum conserved when external torque is zero?

Yes. In the absence of external torque, angular momentum remains constant.

Q9. Why does a rotating disc store more energy at higher speed?

Rotational kinetic energy depends on ω². Hence energy increases rapidly with speed.

Q10. Can friction do zero work in rolling motion?

Yes. In pure rolling, the point of contact is momentarily at rest, so friction does no work.

Next: Stage 2 – Page 3
Long Answer Questions & Derivations

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