How is this system in equilibrium?

[Peppino]

[diagram attached]

Assume some friction between M and the surface.

The forces acting on the connector point are the forces of friction of the M blocks and the weight of m, but they are in different directions; how do they manage to cancel out?

 

[CWatters]

By being in opposite directions.

Aside: If the string (?) joining the blocks really was horizontal the tension would be infinite so it must sag a bit. Assume it sags to an angle θ with the horizontal. Then look at the horizontal and vertical components. The vertical components adds to the normal force on the blocks. The horizontal force is opposed by friction etc.

 

[Peppino]

But the weight of m is perpendicular to the frictional forces

 

[CWatters]

But the weight of m is perpendicular to the frictional forces

There are other vertical forces.

See my earlier reply that I edited.

 

[CWatters]

Can I check the line joining the blocks is indeed something like string and not a rigid rod?

 

[Peppino]

Yes. Sorry I thought that was implied.

Ah, I see now. It is physically impossible for the strings to be 100% perpendicular, correct?

 

[CWatters]

Yes because the Tension in the string is T = mg/sin(θ) and sin(θ) approaches zero. Perhaps draw it with the string forming a V and work out all the forces.