Rotational Motion – Stage 2 (Page 10)

Assertion–Reason & Mixed Concept Objective Questions

This page is extremely important for Board competitive sections and JEE Main Assertion–Reason questions. Read assertion and reason carefully before choosing the option.

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Directions:

Choose the correct option:
A) Both A and R are true, and R is the correct explanation of A
B) Both A and R are true, but R is not the correct explanation of A
C) A is true, R is false
D) A is false, R is true

Q1.

Assertion (A): A solid sphere rolls down an incline faster than a hollow sphere.

Reason (R): Moment of inertia of a solid sphere is less than that of a hollow sphere.

Correct Answer: A
Explanation: Lower moment of inertia gives greater acceleration in rolling.

Q2.

Assertion (A): Angular momentum of a particle depends on the choice of origin.

Reason (R): Angular momentum is given by L = r × p.

Correct Answer: A
Explanation: r changes with origin, hence angular momentum changes.

Q3.

Assertion (A): Torque acting on a body is zero when angular momentum is constant.

Reason (R): Torque is equal to rate of change of angular momentum.

Correct Answer: A
Explanation: τ = dL/dt → constant L means zero torque.

Q4.

Assertion (A): Friction is necessary for rolling motion.

Reason (R): Friction provides torque required for rolling.

Correct Answer: A
Explanation: Without friction, rolling cannot start.

Q5.

Assertion (A): Moment of inertia of a body can be zero.

Reason (R): Moment of inertia depends on mass distribution about axis.

Correct Answer: B
Explanation: For a point mass on axis, I = 0. Reason is true but not explanation.

Q6. (Mixed Concept)

A wheel rolls without slipping. Velocity of the centre is v. What is the velocity of the topmost point?

Answer: 2v
Method: v_top = v (translation) + v (rotation)

How to Solve Assertion–Reason Questions

✔ First judge Assertion independently
✔ Then test Reason independently
✔ Finally check logical connection
✔ Never rush—examiner designs close options

Stage 2 (Boards + Objective) COMPLETED ✅
Next: Phase 1 – IIT/JEE Solved Problems (Basic → Moderate)

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