A gramophone disc is set revolving in a horizontal plane at the rate of `33(1)/(2)` revolutions per minute. It is found that a small coin placed on the disc will remain there if its centre is not more than 5 cm from the axis of rotation. Calculate the coefficient of friction between the coin and the disc
[Hint : Centripetal force `= m omega^(2)r=` Frictional force `= mu N=mu mg`]