Răspuns: c) 100 J
Explicație:
energia potentiala gravitationala Ep = mgh
m = masa - in kilograme
g = acceleratia gravitationala≈ 10 N/kg
h = inaltimea la care se afla fata de referinta - metri
varianta 1 .
Ep₁ = mgh₁
h₁ = Ep₁ : (mg) = 140J : ( 2 kg x 10 N/kg) = 7 m
h₂ = h₁ - 2 m = 7 m - 2 m = 5 m
Ep₂ = mgh₂ = 2 kg x 10 N/kg x 5 m = 100 J
Varianta 2
Δ Ep = Ep₁ - Ep₂ = mgh₁ - mgh₂ = mg ( h₁ - h₂)
m = 2 kg
g = 10 N/kg
h₁ - h₂ = 2 m
ΔEp = 2 kg x 10 N/kg x 2 m = 40 J
Ep₂ = Ep₁ - ΔEp = 140 ΔJ - 40 J = 100 J
