A long horizontal rod has a bead which can slide along its length and is initially placed at a distance L from one end A of the rod.

Hi, I have a question and I hope anyone could answer it:

A long horizontal rod has a bead which can slide along its length and is initially placed at a distance L from one end A of the rod. The rod is set in angular motion about A with a constant angular acceleration α .If the coefficient of friction between the rod and bead is µ, and gravity is neglected, then the time after which the bead starts slipping is

(a) (sqrt{frac{mu}{alpha}})

(b) (frac{mu}{sqrt{a}})

(c) (frac{1}{sqrt{mu, alpha}})

(d) Infinitesimal