Question

A gramophone record is revolving with an angular velocity ω. A coin is placed at a distance r from the centre of

the record. The static coefficient of friction is μ. The coin will revolve with the record if


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Answer 1

r  ≤ μg/ω2

Explanation: the coin will revolve with the record, If force of friction  ≥  Centrifugal force

μmg  ≥ mrω2

r ≥  μg/ω2

Let the mass of the coin be m. The coin will revolve with the record if the frictional force which supplies the centripetal force (required for the circular motion of the coin) is sufficient. Since the maximum value of the frictional force is μmg, we have

μmg ≥ mrω2

Therefore r ≤ μg/ω2.

Answer 2

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Answer:

Correct option (c) r ≤ μg/ω2 Explanation: the coin will revolve with the record, If force of friction ≥ Centrifugal force μmg ≥ mrω2 r ≥ μg/ω2