Discussion and hints:

Recall the following four-step plan outline in the lecture book and discussed in lecture:

Step 1: FBD
Draw a free body diagram of the system made up of A+P.

Step 2: Kinetics (linear impulse/momentum and work/energy)
From your FBD above, what is the external force acting on the system of A+P in the horizontal direction? What does this say about the linear momentum of this system in that direction? Also, are there any non-conservative forces acting on the system of A+P? What does this say about the mechanical energy of the system?

Step 3: Kinematics
The motion of P as seen by an observer on A is directed along the angle θ of the wedge. Write down the kinematics vector equation of v_P = v_A + v_P/A. This provides two scalar equations that represent the constraint of motion between A and P.

Step 4: Solve
Solve for the speeds of A and P from the above equations.

Question: Watch the animation above. Note that the actual path of P is at an angle that is different from the wedge angle θ – why is that?

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Any questions?