The elastic potential energy stored in a steel wire of length 20 m stretched through 2 cm is 80 J. The cross sectional area of the wire is ____ mm^2.…

The elastic potential energy stored in a steel wire of length $\displaystyle 20$ m stretched through $\displaystyle 2$ cm is $\displaystyle 80$ J. The cross sectional area of the wire is $\displaystyle \_\_\_\_$ $\displaystyle \mathrm{mm}^2$. (Given, $\displaystyle \mathrm{y}=2.0 \times 10^{11} \mathrm{Nm}^{-2}$ )