impulsul p = 20 kg m/s
Δt = 5 s
F = 8 N
Ec2 / Ec1 = ?
Ec₁ = mv₁² / 2
Ec2 = mv₂² / 2
Ec2 / Ec1 = mv₂² / mv₁² = v₂² / v₁²
stim ca F = ma , a = Δv/Δt
F = m Δv/ Δt
FΔt = mΔv = mv₂ - mv₁
dar mv₁ = p = impulsul initial
FΔt = mv₂ - p
mv₂ = FΔt + p =(5x8) N s + 20 kg m/s =
= 40 kg s / m/s² +20 kg m/s = 60 kgm/s
v₂ = (60 kgm/s) / m = (60 / m ) m/s
v1 = p/m = [(20 kgm/s) / m ] m/s
Ec2 / Ec1 = v₂² / v₁² = (60/m)² / (20/m)² = (60/20)² = 9
