If a mass ' \(m\) ' oscillates on a spring having a mass \(m_{s}\) and stiffness ' \(k\) ', then the natural frequency of the system is given by

(a) \(\sqrt{\frac{k}{m+\frac{m_{s}}{3}}}\)

(b) \(\sqrt{\frac{k}{\frac{m}{3}+m}}\)

(c) \(\sqrt{\frac{3 k}{m+m_{s}}}\)

(d) \(\sqrt{\frac{k}{m+m_{s}}}\)