What is the slope of the graph of stress $\to$ strain up to the elastic limit?

$A$ vertical hanging bar of length $l$ and mass $m$ per unit length carries a load of mass $M$ at its lower end. Its upper end is clamped to a rigid support. The tensile stress at a distance $x$ from the support is (where $A$ is the area of cross-section of the bar):

$Assertion :$ Strain causes the stress in an elastic body.
$Reason :$ An elastic rubber is more plastic in nature.

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 $5 \times 10^{-4}$.

The length of an elastic string is $a$ metres when the longitudinal tension is $4 \ N$ and $b$ metres when the longitudinal tension is $5 \ N$. The length of the string in metres when the longitudinal tension is $9 \ N$ is

$A$ and $B$ are two wires. The radius of $A$ is twice that of $B$. They are stretched by the same load. Then the stress on $B$ is