1. The problem statement, all variables and given/known data An elevator goes down with a constant acceleration a. Someone throws the ball upward from the floor with an initial velocity u relative to the elevator. If the height of the elevator is h=2,25m, the ball has an initial speed relative to the elevator u=15 m/s and it hits the ceiling of the elevator in an elastic way, find the time needed to reach the ceiling and that one spent to get to the floor again. 2. Relevant equations Let's call a' the relative acceleration of the ball with respect to the elevator.Then: a'=g-a h=ut-1/2 a' t2 Would someone tell me explicitly the reasoning, please?