A vibration pickup has been designed for operation above a frequency level of \(100 \mathrm{~Hz}\) without exceeding an error of \(2 \%\). When mounted on a structure vibrating at a frequency of 100 \(\mathrm{Hz}\), the relative amplitude of the mass is found to be \(1 \mathrm{~mm}\). Find the suspended mass of the pickup if the stiffness of the spring is \(4000 \mathrm{~N} / \mathrm{m}\) and damping is negligible.