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A disc is rotating with angular velocity ω. If a child sits on it, what is conserved?

1. (a) Linear momentum
2. (b) Angular momentum
3. (c) Kinetic energy
4. (d) Moment of inertia

Correct answer: (b) Angular momentum

Solution

When no external torque acts on the system, angular momentum is conserved. The child sitting on the disc does not introduce an external torque, so angular momentum remains constant.

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