Pulley B hangs from the ceiling and has a diameter d. A string twined about the pulley leads around pulley A, hanging from the ceiling, and to a mass M. A beam of length L is attached to the pulley B itself and stretches out horizontally. A mass m is connected to the end. The system is in static equilibrium. (See figure.)
What is the magnitude of the torque due to the weight of mass m about the axis of pulley B?