A heavy steel ball held in contact with an extremely light steel ball at height h  $=5\sqrt{3}$ above a hard horizontal floor. The line joining the centres of the balls makes angle $\theta ={30}^0$ with a vertical. If all the collisions are elastic and sizes of the balls are negligible as compared to the height h, the horizontal range of the lighter ball is R, (radius of the ball is much smaller than horizontal range R). Speed just after collision is u. Then,  
$g=10m/{\sec }^2$