Two fixed friction less inclined plane making $30^{\circ}$ and $60^{\circ}$ with vertical are shown . Two blocks A and B are placed on the two planes . What is the relative vertical acceleration of a with respect to B.

Question

$\begin{array}{1 1} g \\ \large\frac{g}{3} \\ zero \\ \large\frac{g}{2} \end{array}$