A 320-g ball and a 400-g ball are attached to the two ends of a string that goes over a pulley with a radius of 8.7 cm.Because of friction in its axle,the pulley does not begin to rotate.What is the magnitude of the frictional torque at the axle of the pulley if the system remains at rest when the balls are released?
A)0.068 N ∙ m
B)0.61 N ∙ m
C)0.079 N ∙ m
D)0.063 N ∙ m
E)0.00070 N ∙ m

Question

Quizplus · Accepted Answer

The frictional torque is equal to the difference in gravitational force on the two masses times the radius of the pulley. The difference in force is (0.4 kg - 0.32 kg) * 9.8 m/s² = 0.784 N. The torque is 0.784 N * 0.087 m = 0.068 N ∙ m.

A 320-G Ball and a 400-G Ball Are Attached to the Two