Block A in the figure weighs 1.50 N and block B weighs 3. The coefficient of kinetic friction between all surfaces is 0.

Block A in the figure weighs 1.50 N and block B weighs 3.90 N. The coefficient of kinetic friction between all surfaces is 0.500. Find the magnitude of the horizontal force vec F_a necessary to drag block B to the left at a constant speed of 7.00 cm/s if A rests on B and moves with it (figure a)?Find the magnitude of the horizontal force vec F_b necessary to drag block B to the left at a constant speed of 7.00 cm/s if A is held at rest by a string (figure b)?In part (A), what is the friction force on block A?