Two inclined planes OA and OB having inclination (with horizontal) ${30}^0$  and  ${60}^0$ respectively, intersect each other at O as shown in figure. A particle is projected from point P with velocity  $u=10\sqrt{3}m{s}^{-1}$ along a direction perpendicular to plane OA. If the particle strikes plane OB perpendicularly at Q, calculate:

Find time of flight = ?  $(g=10 m/s^2)$