The force $P$ is applied to the bar, which is made from an elastic perfectly plastic material.

Construct a graph to show how the force in each region $AB$ and $BC($vertical axis$)$ varies as $P$

$($horizontal axis$)$ is increased. The bar has cross$-$sectional areas of $1i{n}^2$ in region $AB$ and $4i{n}^2$ in

region $BC.$ Take ${}_y=30$ksi.