Two particles A and B each of mass m are attached by a light inextensible string of length 2l. The whole system lies on a smooth horizontal table with B initially at a distance l from A. The particle at the end B is projected across the table with speed is perpendicular to AB. velocity of ball A just after the **** is

Question

 

$$\begin {array} {1 1} (a)\;\frac{u \sqrt 3}{4} & \quad (b)\;u \sqrt 3 \\ (c)\;\frac{u \sqrt 3}{2} & \quad  (d)\;\frac{u}{2} \end {array}$$