A fixed pulley carries a weightless thread with masses m1 and m2 at its ends. There is

Question:

A fixed pulley carries a weightless thread with masses m1 and m2 at its ends. There is friction between the thread and the pulley. It is such that the thread starts slipping when the ratio m2/ml =ηo. Find:
(a) The friction coefficient;
(b) The acceleration of the masses when m2/ml = η > ηo