The elastic limit for a gas

$A$ steel wire having a radius of $2.0 \, mm$, carrying a load of $4 \, kg$, is hanging from a ceiling. Given that $g = 3.1\pi \, m/s^2$, what will be the tensile stress that would be developed in the wire?

The elastic behaviour of a material for linear stress and linear strain is shown in the figure. The energy density for a linear strain of $5 \times 10^{-4}$ is $\dots \; kJ/m^3$. Assume that the material is elastic up to the linear strain of $5 \times 10^{-4}$.

If under an external force,a change in length $\Delta l$ occurs in a rod of original length $l$,then write the formula for longitudinal strain.

$A$ wire of length $l$ and cross-sectional area $A$ is stretched by a weight $Mg$ such that its length becomes double. What is the stress in the wire?

When a heavy weight is suspended from a metal wire and then removed,the wire does not regain its original length. Why?