⚛️ Physics · System of Particles and Rotational Motion · NEET & JEE

A disc of moment of inertia 4 kg·m2 rotates at 10 rad/s. A lump of clay is dropped onto its edge, adding 1 kg·m2 to the moment of inertia. The new angular velocity is:

Answer: 8 rad/s.

A 10 rad/s
B 8 rad/s
C 5 rad/s
D 4 rad/s

Correct answer: B. 8 rad/s

Explanation: Angular momentum is conserved: I1ω1 = I2ω2, so 4 × 10 = 5 × ω2, giving ω2 = 8 rad/s.

Torque about axis O equals the force F multiplied by the perpendicular distance r⊥ from the axis to the line of action of the force, producing rotation.

Concept context

Moment of inertia, torque, angular momentum, rolling motion. Very high JEE weightage.

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A disc of moment of inertia 4 kg·m<sup>2</sup> rotates at 10 rad/s. A lump of clay is dropped onto its edge, adding 1 kg·m<sup>2</sup> to the moment of inertia. The new angular velocity is:

Concept context

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