A girl sitting on a spinning bus tool with her legs folded , suddenly out spreads then her angular velocity will:
Correct answer: A. decrease
- A. decrease
- B. increase
- C. Remain the same
- D. first increase and then decrease
Explanation
The moment of inertia of girl increases (since the mass of her legs is now farther from the axis of rotation). According to the law of conservation of angular momentum, the product of the moment of inertia and the angular velocity must remain constant. If the moment of inertia increases, the angular velocity must decrease in order to keep the total angular momentum constant. So the correct answer is (A) decrease.
This question appeared on the ETEA MDCAT 2009 paper, which you can sit online with every answer explained.
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About Angular Velocity
Angular velocity describes how quickly angular displacement changes with time, with ω = Δθ/Δt and units of radians per second. Questions relate angular and linear motion through v = rω, use the direction given by the right hand rule, and distinguish angular velocity from angular acceleration and ordinary frequency.
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