Rotational Motion – Stage 2 (Page 8)

Objective Questions – Advanced Application (With Explanations)

These questions test deep understanding of rotational dynamics. They are frequently asked in JEE Main, AP/TS Board objective sections.

Q19.

A disc is rotating freely. If its moment of inertia is suddenly doubled, its angular velocity becomes:

A) ω
B) ω/2
C) 2ω
D) Zero

Correct Answer: B
Explanation: Angular momentum L = Iω is conserved. If I doubles, ω becomes half.

Q20.

A solid sphere and a hollow sphere of same mass and radius roll down an incline without slipping. Which has greater angular acceleration?

A) Solid sphere
B) Hollow sphere
C) Both same
D) Depends on mass

Correct Answer: A
Explanation: Solid sphere has smaller moment of inertia → higher angular acceleration.

Q21.

A flywheel stores energy due to:

A) Translational motion
B) Rotational motion
C) Elastic deformation
D) Friction

Correct Answer: B
Explanation: Flywheel stores energy as rotational kinetic energy.

Q22.

Which graph represents torque vs angular acceleration?

A) Straight line through origin
B) Parabola
C) Hyperbola
D) Random curve

Correct Answer: A
Explanation: τ = Iα ⇒ linear relation.

Q23.

If a body has zero angular momentum, it must be:

A) At rest
B) Not rotating
C) Moving linearly
D) Cannot be determined

Correct Answer: D
Explanation: Angular momentum depends on reference axis.

Q24.

A rotating body has constant angular momentum. Which quantity must be zero?

A) Angular velocity
B) Torque
C) Angular acceleration
D) Moment of inertia

Correct Answer: B
Explanation: dL/dt = τ. For constant L, τ = 0.

Q25.

A disc rolls without slipping. The ratio of translational KE to rotational KE is:

A) 1 : 1
B) 2 : 1
C) 1 : 2
D) 3 : 1

Correct Answer: B
Explanation: For disc: I = ½MR² → KE_trans : KE_rot = 2 : 1.

Q26.

Which physical quantity is conserved in a perfectly elastic collision about the center of mass?

A) Linear momentum
B) Angular momentum
C) Kinetic energy
D) All of these

Correct Answer: D
Explanation: All are conserved in elastic collision.

Advanced MCQ Solving Tips

✔ Use conservation laws first
✔ Compare moments of inertia
✔ Avoid assuming axis incorrectly
✔ Always check reference point

Next: Stage 2 – Page 9 (Assertion–Reason & Multi-Concept MCQs)

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