Answer
1/2 m v^2 = m g H by conservation of energy for an object fired straight up or
H = v^2 / (2 * g)
For an object traveling at 45 deg then
Vy = V sin 45 = 2^1/2 / 2 * V
So now
H = 1/2 * v^2 / (2 * g) = v^2 / (4 * g)
and the projectile will travel H / 2 instead of H