Concurrent Forces, Cables & Two-Force Members

When every force passes through one point, the moment equation says nothing and two force equations do all the work. Cables, rings, hooks and the pins of a truss are all solved this way.

Worked: a sign on two cables

Horizontally, T₁ cos 30° = T₂ cos 45°, so T₁ = 0.816 T₂. Vertically, T₁ sin 30° + T₂ sin 45° = 600, so 0.408 T₂ + 0.707 T₂ = 600 and T₂ = 538 lb, T₁ = 439 lb. Lami agrees: T₁ = 600 sin 135°/sin 105° = 439 lb.