Block A in the figure weighs 1.70 N and block B weighs 4.60 N. The coefficient of kinetic friction between all surfaces is 0.400. Find the magnitude of the horizontal force vec F_a necessary to drag block B to the left at a constant speed of 4.50 cm/s if A rests on B and moves with it (figure a).In part (A), what is the friction force on block A?