A steel frame supports a turbine -driven exhaust fan. At a speed of 400 rpm, the amplitude of motion is 4.5 mm measured at the floor level of the fan.

At a speed of 500 rpm, the amplitude is 10 mm. No resonant condition is observed in changing speed from 400 to 500rpm. To decrease this intolerable vibration, it is proposed to add a slab of concrete beneath the turbine. The mass of the slab is chosen such that the total mass of the system with the fan is doubled. Does this solve the vibration problem?