Question

A gramophone record is revolving with an angular velocity $\omega$. A coin is placed at a distance $r$ from the centre of the record. The static coefficient of friction is $\mu$. The coin will revolve with the record if

• A. $r=\mu g\omega^2$
• B. $r < \frac{\omega^2}{\mu g}$
• C. $r \le \frac{\mu g}{\omega^2}$
• D. $r \ge \frac{\mu g}{\omega^2}$

Answer 1

Answer: (C)

$r \le \frac{\mu g}{\omega^2}$

Answer 2

The coin will revolve with the record, if Force of friction $\le$ Centrifugal force
$\mu mg \ge mr\omega^2$
or $r\le \frac{\mu g}{\omega^2}$