Consider a quarter circular smooth rod AB fixed AB fixed in a vertical plane with centre of the circle at O. A bead of mass m slides without friction with the help of string starting from point A under the action of a constant force `F = 2 gm` as shown in figure.
The velocity of bead when string makes an angle `30^(@)` with the horizontal is nearly :
A. `sqrt(g R (4 sqrt2 - 5))`
B. `2 sqrt(gR)`
C. `sqrt(g R (5 - 2 sqrt3))`
D. `5 sqrt (gR)`