A ring of mass M and a block of mass m are in equilibrium. The string is light, the pulley is frictionless, and the coefficient of friction between the pole and the ring is μ. The frictional force exerted by the pole on the ring is:

Question

G1 Physics · Accepted Answer

The string segment attached to the ring is horizontal, so tension has no vertical component on the ring. The only downward vertical force on the ring is Mg; therefore static friction supplied by the pole must be Mg upward. Hence option A.