I can't figure this one out: A mass moves in a circle with radius of 5.7 m due to a centripetal force of 487 N. The mass takes 1.1 seconds to complete a loop. The centripetal force is then reduced to a quarter of its original value. How long will it take to complete a loop with the same 5.7 m radius? Round to the nearest tenth.

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.