From this: http://www.collegeboard.com/prod_downloads/ap/students/physics/ap06_frq_physics_c_mech.pdf Question 1 is what I'd like to ask about :) For part a, for the block it would be a simple mg down, F N up and Ff to the left... For the Slab, do we include the fact that it's pushing up on the block and that the block is pushing down on it, or do we just include the usual mg and FN? Part b, I would think linear momentum is conserved, so: mB v0 = mB vf - mS vf, negative mS vf because the slab would move to the left, right? Well, for some reason, when I solve from there, I get a negative vf. Very very fishy... For part c, do I assume the change in kinetic energy of the block is equal to the work done by the slab, so delta K = Ff * D and solve for D? d) I'm going to guess change in kinetic energy... I hope someone can clarify how to do this question, as it confuses the hell out of me.. I appreciate any responses.