A bead slides on a circular wire

[minmm]

Homework Statement

A bead slides on a smooth circular wire of radius b which lies in a vertical plane. The bead starts from rest at a point that is level with the center of the hoop.
Find the time it takes for the bead to slide to the bottom of the hoop.

The attempt at a solution
at t=0
U=mgb, KE=0

at the bottom
U=0, KE=mv²/2, v=(2bg)^1/2

 

[LawrenceC]

What about the time?