vx/vy=tanβ
h=vy^2/(2g)
vx=v0
所以，當物體被拋出時，它的動能與重力勢能之比:
(1/2mv0^2)/(mgh)=(1/2mvx^2)/[mgvy^2/(2g)]
=(1/2mvx^2)/(1/2mvy^2)
=vx^2/vy^2
=(tanβ)^2