In order to draw the FBDs for the case with friction, you need to know first the direction of impending motion; that is, you need determine whether A moves UP the incline or DOWN the incline, since friction will oppose that motion. To determine the direction of impending motion, solve the problem for the friction-free case first (μk = 0). Once this direction is determined, rework the problem with friction.
Recall the following four-step plan outline in the lecture book and discussed in lecture. You will need to do this for both the friction-free case and the with-friction case.
Step 1: FBDs
Draw individual free body diagrams for the two blocks.
Step 2: Kinetics (Newton’s 2nd Law)
Write down Newton’s 2nd law for each block.
Step 3: Kinematics
Recall the work that we did in Chapter 1 in relating accelerations of two particles connected by a cable-pulley system.
Step 4: Solve
At this point you will have two equations in terms of two unknowns: the normal contact force and the tension force. Solve.
Ask and answer questions here. You learn both ways.