Question

The alternator on a truck engine produces 350Wof electric power when it rotates at 4000 rev/min. If it is 95 percent efficient, what should the difference (in newtons) between the tensions in the tight and slack parts of its V-belt drive be? The diameter of the alternator’s pulley is 10 cm. 

Answer 1

Torque:

$$\tau=\frac P\omega=5.25\text{ Nm}.$$

Tension:

$$T=\frac \tau r=52.5\text{ N}.$$

The difference in tension:

$$\Delta T=T(1-\eta)=2.63\text{ N}.$$