rotation

In the given figure , a smooth parabolic wire lies in the vertical (x-y plane) .The shape of the given track is defined by the equation y=x²/a(a is a constant ) .A ring of mass of which can slide freely on the wire track,is placed at the position A(a,a).The track is rotated with angular velocity ω such that there is no slipping between the ring and the track then ω is equal to

(a)√g/a
(b)√g/2a
(c)√2g/a
(d)2^1/4√g/a