But we do know that the final positions of the two balls must be the same, and the final time when they collide must be the same.
So, the condition on the position of the upward ball so that it is at its maximum height is: x = vo2/(2g) The dropped ball must also be at this position at the same time if the two balls are to meet there.
Simultaneously, a second rubber ball at height h directly above the first ball is dropped from rest. 1. At what height above the ground do the balls collide? Your answer will be a symbolic expression in terms of v0, h, and g .