A machine of total mass 100 kg is mounted on a suspension which has a static deflection under the weight of the machine of 1.5mm. In the rotating parts of the machine there is an out-of-balance force created by a mass of 0.02kg rotating with a 40mm eccentricity. When operating it is necessary to limit the vibration amplitude at resonance to 0.25mm by fitting a viscous damping device in the suspension. Calculate the damping coefficient required.