Block A in the Figure weighs 1.20 N and block B weighs 3.60 N. The coefficient of kinetic friction between all surfaces is 0.300. Find the magnitude of the horizontal force F necessary to drag block B to the left at a constant speed of 2.50 cm/s (a) if A rests on B and moves with it (Figure a); (b) if A is held at rest by a string (Figure b). (c) In part (a), what is the friction force on block A? y Figure a A B Figure b A B Figure a n W fk 91