A ball is thrown vertically up from the ground with a speed v0. At the same instant, a second ball is dropped from rest from a height H, directly above the point where the ball was thrown.

There is no air resistance.

i) Find the time at which the two balls collide.

ii) Find the value of H, in terms of v0 and g, such that at the instant when the two balls collide, the first ball is at the highest point of its motion.

I'm struggling with part i). I've tried considering different Frames of Reference to make it easier but I still know how to work it out.

Any help would be greatly appreciated!

Thanks