Work done $=$ Force $\times$ elongation

$W=F \cdot \Delta x \ldots .$  $\left\{F=\Delta x \cdot \frac{A Y}{L}\right\}$

$\Rightarrow W=\frac{A Y}{L} \times \Delta x^2$

Multiply and divide by $L$

We get

$W=\frac{\text { Volume } \cdot Y}{L^2} \Delta x^2$

Cross multiply ( $L \cdot A)$ volume

$\frac{W}{L \cdot A}=Y \cdot\left(\frac{\Delta x}{L}\right)^2$

Work done per unit volume

Substitute values

$=8 \times 10^{10} \cdot\left(\frac{2}{100}\right)^2$

$=32 \,MJ / m ^3$