# Kinetic Friction

by Heat
Tags: friction, kinetic
 P: 273 1. The problem statement, all variables and given/known data Consider the system shown in the figure. Block A has weight w_A and block B has weight w_B Once block B is set into downward motion, it descends at a constant speed. Calculate the coefficient of kinetic friction between block A and the table top. A cat, also of weight w_A, falls asleep on top of block A. If block B is now set into downward motion, what is the magnitude of its acceleration? Express your answer in terms of w_A, w_B and g. 2. Relevant equations F=ma w=ma 3. The attempt at a solution I know that when the box is sliding at constant speed the kinetic friction is: Fsubk = $$\mu$$subk n . The thing is I don't know where to start, as there are no numbers. I would know that the block b is gravity pulling down.