Physics problem - I need help figuring it out (friction, forces)

[joshdoe]

I'm having trouble figuring this physics problem out; I was hoping someone here could help me. I drew a quick diagram of the problem here.

A block (B) of weight 2w is sliding down an incline (I) of x° at a constant rate. A plank (P) of weight w rests on top of the block, tied to a wall. If the coefficient of friction is the same between the block and the incline, and the block and the plank, what is the coefficient?

So far I've figured it out to have seven forces acting in the block, but I'm not sure. Anyone?

 

[joshdoe]

Let me see, theres Fn, Fp, Fd, two Ff, Fp and Fd of the plank. Or is it only Fp for the plank?

 

[Unsickle]

Solution Here

Tell me if you need more explanation.

 

[joshdoe]

I think I've got it, thanks.

Just so I'm clear, what are all the forces at work on the block? There's force down (parallel to ramp) and force pressure (perpindicular) determined by the weight of the block. Force normal (perp), and the two frictions (para). Does the plank exert just pressure (perp) on the block, or is there a downward force (para) as well? I'm tending to think it's the former.