1. The problem statement, all variables and given/known data Block A, with weight 3w, slides down an inclined plane S of slope angle 36.9 degrees at a constant speed while plank B, with weight w, rests on top of A and is attached by a cord to the wall. If the coefficient of kinetic friction is the same between A and B and between S and A, determine its value. 2. Relevant equations 3. The attempt at a solution I have some trouble doing the free body diagram for A, I assume the forces acting on said block are: NB, wA, static friction between S and A, but Im not sure about the friction between A and B.