A stone is tied to one end of a light inextensible string of lengthl and made to rotate on a vertical circle keeping other end of the string at the centre. If speed of stone at the highest point is v (v > (gl)^1/2) then its speed at the lowest point is:-


a) (4gl)^1/2
b) (v²+2gl)^1/2
c) (v²+gl)^1/2
d) (v² + 4gl)^1/2
Kindly answer sir/mam.