Hi, I have a physics problem where I am shown two frictionless inclines, each with a box (of the same mass and with the same initial velocity). The two inclines are of different lengths, however (one has a height of H, the other has a height of H1 with H2 being the position of the box at its maximum height). The second incline is shorter than the first.

I am given the values:
initial velocity of both boxes = 7.00m/s
angle theta of incline = 50 degrees
H1 = 1.25 m

I am asked to calculate the total height H1 + H2 for the block on the shorter track.

I am not sure exactly how this forum works, but I hope I explained this well and I am not asking for the answer. I have seen part of solution which uses conservation of energy to calculate the height but I dont understand part of it.

It is Einitial = Efinal
inital Potential + initial Kinetic = Final potential + final kinetic
1/2m(v1)^2 + mgH1 = mg(H1+H2) + 1/2m(v1 cos theta)^2

v1 is the velocity of the box at the height of H1,
so v1cos theta must be velocity at H2.

I dont understand why the velocity at H2 must take into account the angle theta but not the height at H1. Also, since H2 is supposed to be the maximum height of the box, shouldn't the velocity be zero (instantaneosly) at the top? Any help with understanding this would be much appreciated.