See the diagram: [PLAIN]http://img31.imageshack.us/img31/6959/vwork.png [Broken] The diagram is an ideal mechanical system of massless beams. The platform C holds a weight of "W". There are gear-motor mechanisms at connections A and B, which provide internal torques. Suppose, the smaller (acute) angle between beam OA and horizontal is θ. The mechanism at A provides an initernal torque to maintain the smaller angle BAO = 2θ. The mechanism at B provides an initernal torque to maintain the smaller angle ABC = 3θ. Using principle of virtual work (δU=0), find the minimum moment M which must be applied at O to raise the load W. Please help in solving the above problem. I cannot find a way to calculate the virtual work done by W when the virtual work done by M is Mδθ. Also what will happen to the internal torques provided. Will they appear in the moment M expression? Thanks for the help.