Supporting a trapezoid between two wedges

[Tom Hammer]

Homework Statement

Find the weight W that can be supported by the applied force of 5 kN. Mu = .25 at all surfaces

Relevant Equations

F = mu N, where mu = coefficient of static friction, N = normal force

Let Nr = normal force on the right side of the trapezoid B and Fr = the force of friction on the right side of B.
Let Nl = normal force on the left side of B and Fr = the frictional force on the left surface of B

so Nr = 5 sin45 and Fr = 5 sin45 =
and Nl = 5 sin 60, Fl = 5 sin 30.

 

[haruspex]

All surfaces would include the underside of A.
Consider balance of forces on A and balance of forces on B.

 

[Tom Hammer]

Yes, thank you. But I am having trouble drawing a force diagram which makes sense at the two surfaces of B.

 

[Tom Hammer]

Yes, thank you. But I am having trouble drawing a force diagram which makes sense at the two surfaces of B.

 

[haruspex]

Yes, thank you. But I am having trouble drawing a force diagram which makes sense at the two surfaces of B.

Not sure why. What forces act on B?
What forces act on A?
If the system slips, can it do so without sliding at all contact surfaces?

 

[Lnewqban]

Yes, thank you. But I am having trouble drawing a force diagram which makes sense at the two surfaces of B.

Why do you find it difficult?
Forgetting for a moment about block A, only three forces acting perpendicularly to each of the top and side surfaces of B are needed to keep in equilibrium.
Try a vectorial addition of those forces, which should form a triangle.