A mass weighing 10 kgf is supported by a spring of stiffness 20 kgf / cm and a viscous damper. During free vibrations, the amplitude of vibrations decreases to one-tenth of its initial value in two complete oscillations. Find the value of damping coefficient of the damper. If a sinusoidal force of amplitude 15 kgf and frequency 600 cycles / minute acts on the mass, find the amplitude and phase of the (a) motion of the mass and (b) force transmitted to the support.