Dynamics Question Involving two blocks on a plane

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SUMMARY

The discussion revolves around solving a dynamics problem involving two blocks on a plane, specifically analyzing the forces acting on the system. The participant utilized Newton's second law (F=ma) and derived an inequality involving the angles and forces, ultimately leading to the expression: tan x > (2um1 + um2) / (m2 - m1). The participant identified a potential error in their approach regarding the frictional forces, particularly questioning the dependence of friction on the mass of the second block (m2) when the system is stationary.

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Homework Statement



http://i.imgur.com/K2hYHgq.png
Picture here with question.

Homework Equations



F=ma

The Attempt at a Solution



For the system to begin moving, a>0 therefore

Fnet>0

I drew some FBDs and came up with four relevant forces total; the force of gravity along the plane for each of the two blocks, and the force of friction on the plane by m1 and m2, and the force of friction on m1 by m2. I ended up with something like this (g is cancelled):

m2sinx - m1 sinx - um1cosx - u(m1+m2)cosx > 0

tan x > (2um1+um2)/(m2-m1)

And solved for x from there.

However, my answer is wrong. I think I'm getting stuck with the forces of friction, the denominator in my expression (m2-m1) seems very reasonable considering the system should act similarly to a block of mass m2-m1 with the extra force of friction.
 
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If your equation is from a FBD of m1 you may want to reconsider which mass is involved in the expression for the frictional force. (hint: if the system is not moving, can the force of friction then depend on m2?)
 
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