a) Ft = G sin h/l = 50N·1/2 = 25N;
Fr = 8,33N. Inseamna ca forta necesara este suma celor doua, dar de sens contrar:
F = Ft + Fr = 25N + 8,33N = 33,33N
b) Lc = F·d = 33,33N × 6m = 199,98 = 200J
c) Lu = mgh = 5kg X 10N/kg x 3m = 150J
η = Lu/Lc = 150J/200J = 3/4 = 0,75 = 75%