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Concepts Of Physics MCQ Edition [Volume 1]PhysicsRotational Mechanics

A person sitting securely on a rotating stool has his arms extended. If he folds his arms, what happens to his angular momentum about the axis of rotation?

Options

  1. AIt remains unchanged
  2. BIt decreases
  3. CIt increases
  4. DIt doubles

Correct answer

A. It remains unchanged

Step-by-step solution

Since no external torque acts on the system about the axis of rotation, the angular momentum of the system must be conserved. According to the law of conservation of angular momentum, L = I = constant . When the person folds his arms, his moment of inertia I decreases. To conserve angular momentum, his angular velocity increases, but the total angular momentum L remains unchanged.

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