Răspuns:
3)
Ea = ma×va²/2 => 2Ea = ma×va²
Eb = mb×vb²/2 => 2Eb = mb×vb²
mb = 2ma
vb = va/2
2Eb = 2ma×(va/2)²
2Eb = 2ma×va²/4
2Eb/2Ea = (2ma×va²/4)/(ma×va²)
simplificam
Eb /Ea = 1/2
4)
Ec = mv²/2
m = 3t = 3000 kg
v = 72km/h = 72000m/3600s = 20m/s
Ec = 3000kg×(400m²/s²)/2 = 600 000 J
