The coefficients of friction between a block of mass 0.5 kg and a surface are μs = 0.75 and μk = 0.45. assume the only other force acting on the block is that due to gravity. what is the magnitude of the frictional force (in newtons) on the block if the block is at rest and the surface is horizontal? use g = 9.79 m/s2

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.