Answer
7.2 J
Work Step by Step
Hooke's law states
$F_{x}=-kx$
$\implies k=-\frac{F_{x}}{x}=-\frac{-360\,N}{+4.0\times10^{-2}\,m}$ (restoring force is taken as negative)
$=9.0\times10^{3}\,N/m$
$W_{s}=\frac{1}{2}kx_{i}^{2}-\frac{1}{2}kx_{f}^{2}$
$=\frac{1}{2}k(x_{i}^{2}-x_{f}^{2})$
$=\frac{1}{2}\times9.0\times10^{3}\,\frac{N}{m}((5.0\times10^{-2}\,m)^{2}-(3.0\times10^{-2}\,m)^{2})$
$=7.2\,Nm=7.2\,J$
