Assertion and Reason: Coin on a Gramophone – Rankers Physics

Uniform Circular Motion: Practice Problem & Solution

Assertion (A): A coin is placed on the gramophone. When the motor starts, the coin moves along the gramophone. As the speed goes on increasing, the coin flies off after some time. Reason (R): The gravitational force of gramophone provides the necessary centripetal force to the coin.
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Uniform Circular Motion. Understanding the underlying formula is key to arriving at the correct answer below:

Assertion (A) is true: As the angular speed \( \omega \) of the gramophone increases, the required centripetal force \( m \omega^2 r \) for the coin increases. When this force exceeds the maximum static friction (\( \mu_s mg \)), the coin slips off.

Reason (R) is false: The centripetal force is provided by the frictional force between the coin and the gramophone, not by the gravitational force. Gravitational force provides the normal force.

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