The 80-lb boy stands on the beam and pulls with a force of 40 lb. If (s)D = 0.4, determine the frictional force between his shoes and the beam and the reactions at A and B. The beam is uniform and has a weight of 100 lb. Neglect the size of the pulleys and the thickness of the beam. 60 13 12 D A B 5 ft -3 ft -4 ft 1 ft