1. The problem statement, all variables and given/known data From a lift moving upward with a uniform acceleration 'a', a man throws a ball vertically upward with a velocity v relative to the lift.The ball comes back to the man after a time 't' Show that a+g = 2v/t 2. Relevant equations s=ut+1/2gt2 3. The attempt at a solution I know this is a simple problem. By the substituting values 'v', 't' and a+g as acceleration in the above equation, i could get the answer. All of this is done by considering it from the lift's frame of reference. But I don't understand why we are adding g and a . SHouldn't we subtract them ? the ball goes up and down so must we subtract it the first time and add it the second? really confused.