Răspuns:
2. L=24000J
3. F=45N
Lu=225J
Lc=281.25J
Explicație:
2. P=L/t
P=Fd/t=Fv
v=72km/h=20m/s
L/10=120x20
L=2400x10
L=24000J
3. la scripetele fix F=R R=G=mg, g=10N/kg
F=4.5x10=45N
Lu=Fh=45x5=225J
η=Lu/Lc
80/100=225/Lc
Lc=22500/80
