An engine of mass 1100 kg is supported on a mounting of stiffness 1.3 MN/m and a damper that reduces the amplitude of vibrations to one-quarter of the initial value in two completed oscillations. The engine runs at 450 rev/min and the unbalance force is 2.0 kN. Find the damping ratio and hence the amplitude of the resulting forced vibration. (0.1093, 1.66 mm)