When a ball is released from rest in a very long column of viscous liquid, its downward acceleration is “a” (just after the release). Then its acceleration when it has acquired 3/5 of maximum velocity is  xay, find x + y.

The terminal velocity Vf  of the ball is attained when net force on the ball is zero.The viscous force is = 35WeffHence, net force is Weff−35Weff=25WeffTherefore, the required acceleration is 2a5 .Here x = 2, y = 5, therefore x + y = 7.