On a billiard table two balls B and C are at rest touching each other. A third ball A, travelling with speed u, strikes the two balls elastically (see fig.). Somehow, A hits B first and within a fraction of a second hits ball C. You may assume that B and C are placed symmetrically with respect to the line of motion of A and that all the balls are identical. What angle does the final velocity of A make with its original direction of motion.

Answer

`120^(@)`