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

Which of the following is true for elastic potential energy density

The work done per unit volume to stretch the length of area of cross-section $2 \,mm ^2$ by $2 \%$ will be ....... $MJ / m ^3$ $\left[Y=8 \times 10^{10} \,N / m ^2\right]$

A wire suspended vertically from one of its ends is stretched by attaching a weight of $200\ N$ to the lower end. The weight stretches the wire by $1\ mm$. Then the elastic energy stored in the wire ......... $J$

The work done in increasing the length of a $1$ $metre$ long wire of cross-section area $1\, mm^2$ through $1\, mm$ will be ....... $J$ $(Y = 2\times10^{11}\, Nm^{-2})$

When a block of mass $M$ is suspended by a long wire of length $L$, the length of the wire become $(L+l) .$ The elastic potential energy stoped in the extended wire is :