A rigid rod is placed against the wall as shown in figure. When its velocity of lower end is $10 \;ms^{-1}$ and its base makes an angle $\alpha = 60^{\circ}$ with horizontal, then the vertical velocity of its end B will be :

Question

$\begin{array}{1 1} (1)\; 10 \sqrt{3} \\ (2)\; 10/ \sqrt{3} \\ (3)\; 5 \sqrt{3} \\ (4)\; 5 / \sqrt{3} \end{array}$