A brass rod of 2m is stretched by 1cm have crosssectional area $2cm^2$ .If a force of $10^5$N is applied on it.What is elastic potential energy density?

Question

$\begin{array}{1 1}(A)\;6.2mJ\\(B)\;3.1mJ\\(C)\;1.5mJ\\(D)\;\text{None}\end{array}$