logarithmic decrement of a damped system

Question

The vibrations of a machine of mass 76 kg are damped by a viscous dashpot which diminishes amplitude of vibrations from 17.2 mm to 3.2 mm in two complete oscillations. The machine is mounted on four springs each of stiffness 7.5N/mm. Assuming that the damping force varies as the velocity, determine:

1. The damping
2. The ration of frequencies of damped and undamped vibrations, and
3. The periodic time of damped  vibrations 

Answer 1

Solution based on logarithmic decrement