When the electric motor is resting on the beam, the static deflection of the beam is δs =...

When the electric motor is resting on the beam, the static deflection of the beam is δs = 15 mm. The motor is not perfectly balanced, so when it is operating the unbalanced mass is equivalent to a mass mu = 200 g at a distance of ε = 150 mm from the axis of the rotor. The combined mass of the motor and sprung mass of the beam is mc = 40 kg.

Determine the angular speed of the rotor for resonance to occur. Express your answer in revolutions per minute.

Figure P.73