E = Ep + Ek = mgh + mv^2/2
v^2 = u^2 + 2as = u^2 + 2gh

E0 = 5 × 10 × 20 + 5 × 0^2/2 = 1000 J
E1 = 5 × 10 × 0 + 5 × (0 + 2 × 10 × 20)/2 = 1000 J
E2 = 5 × 10 × -0.1 + 5 × (0 + 2 × 10 × 20.1)/2 = 1000 J


Ако нещо е неясно, питай :]