A ball is thrown straight up from the ground with speed v0. At the same instant, a second ball is dropped from rest from a height H, directly above the point where the first ball was thrown upward. There is no air resistance. How to I find the time at which the two balls collide. A how do I find the value of H in terms of v0 and g so that at the instant when the balls colide, the first ball is at the heighest point of its motion. Anybody who can help?