Question

A coin is placed 21.0 cm from the axis of a rotating turntable of variable speed. When the speed of the turntable is slowly increased, the coin remain fixed on the turntable until a rate of 45 rpm is reached and the coin slides off. What is the coefficient of static friction between the coin and the turntable?

Answer 1

The only force which holds the coin on its position on the rotating table is the force of friction.

Now, when the coin is not sliding, it is following a circular track and the centripetal force is provided by the frictional force.

The centripetal force is given by

And the frictional force is given by

Equating the forces we get

Now, the critical position comes when the angular velocity reaches 45 rpm, the coin starts to move along the radius.

So, putting these values in the equation

So, the coefficient of static friction is 0.476.