A spring-mass system with \(m=25 \mathrm{~kg}\) and \(k=10 \mathrm{kN} / \mathrm{m}\) vibrates on a horizontal surface with coefficient of friction \(\mu=0.3\). Under a harmonic force of frequency \(8 \mathrm{~Hz}\), the steadystate vibration of the mass is found to be \(0.2 \mathrm{~m}\). Determine the equivalent viscous-damping constant of the system.