This problem is trying to find out how much weight can be placed in the middle of a system before the weights on the outside go over the pulleys. A diagram of the problem can be found here http://www.physics.umn.edu/classes/...ds/208321-1201Lab3_P4_Equilibrium_Walkway.pdf We are trying to find d (the distance of the sag) in terms of known quantities. We will know m (the mass of each counterweight), L (the length), and M the mass of the center weight. So far I have... ∑F=Fc+Fa-Fb=0 ƩFx=Fc cosθ+Fa cosθ=0 ∑Fy=Fc sinθ+Fa sinθ-Fb=0 All from the middle point P, where Fb is the force down, Fa is the force up to the left, and Fc is the force up to the right. sinθ=d/L1 =d/√(d2+(L/2)2) That check mark is supposed to be a squareroot if that wasn't clear. I am not sure where to go from here to solve for d.