A) \[r=\mu g{{\omega }^{2}}\]
B) \[r<\frac{{{\omega }^{2}}}{\mu g}\]
C) \[r\le \frac{\mu g}{{{\omega }^{2}}}\]
D) \[r\ge \frac{\mu g}{{{\omega }^{2}}}\]
Correct Answer: C
Solution :
When the disc spins the frictional force between the gramophone record and coin is \[\mu \,mg.\] The coin will revolve with record, if \[{{F}_{frictional}}\ge {{F}_{centripetal}}\] \[\mu \,mg\ge m{{\omega }^{2}}r\] \[\frac{\mu g}{r}\ge {{\omega }^{2}}\]
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