Problem 4.23

A non-deformed spring whose ends are fixed has a stiffness $x=13 \mathrm{~N} / \mathrm{m} .$ A small body of mass $m=25 \mathrm{~g}$ is attached at the point removed from one of the ends by $\eta=1 / 3$ of the spring's length. Neglecting the mass of the spring, find the period of small longitudinal oscillations of the body. The force of gravity is assumed to be absent.