The damping constant of a mass suspended at the free end of a cantilever beam

Question

1. A mass M, of 20 Kg is attached to the free end of a steel cantilever beam of length  1000 mm having a cross-section of 5 ´ 25 mm. Assume the mass of the cantilever to be negligible and E_steel = 200 GPa. If the lateral vibration of this system is critically damped using a viscous damper, the damping constant of the damper is                           

(a) 1250 Ns/m                                                     (b) 625 Ns/m

(c) 312.50 Ns/m                                                  (d) 156.25 Ns/m