A disc rotates with angular speed ω. If a child sits on it and no external torque acts, which quantity is conserved?
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Question

A disc rotates with angular speed ω. If a child sits on it and no external torque acts, which quantity is conserved?

G1 Physics · Accepted Answer

Step 1: The child increases the rotating system inertia while friction may change rotational kinetic energy. Step 2: With zero external torque, L=Iω is conserved. Final answer: B — angular momentum.