As shown below, bob A of a pendulum having massless string of length 'R' is released from $$60^{\circ}$$ to the vertical. It hits another bob B of half the mass that is at rest on a friction less table in the center. Assuming elastic collision, the magnitude of the velocity of bob A after the collision will be (take g as acceleration due to gravity.)

A

$$\frac{4}{3}\sqrt{Rg}$$

B

$$\frac{2}{3}\sqrt{Rg}$$

C

$$\sqrt{Rg}$$

D

$$\frac{1}{3}\sqrt{Rg}$$