Answer
$238,267.7\space kg$
Work Step by Step
Here we use the equation $T=\frac{2\pi}{\omega}=2\pi\sqrt {\frac{m}{K}}$ to find the mass. Where, T - oscillation period, m - mass of oscillation, K - spring constant.
$T=2\pi\sqrt {\frac{m}{K}}$
$T^{2}=4\pi^{2}\times\frac{m}{K}=\gt\frac{KT^{2}}{4\pi^{2}}=m$
Let's plug known values into this equation.
$\frac{0.288\times10^{6}N/m\times(5.715)^{2}}{4\pi^{2}}=m$
$m=238,267.7\space kg$
