$(25$pts$)$ A bronze C$86100$ alloy bar is loaded with a force $P=1$ kipat point $B.$ Ignore the effect of the transition at B and of lateral$/$transverse Poisson's ratio effects. Section AB has a diameter of $0\mathrm{.}75$ in$.$ Section BC is a diameter of $1\mathrm{.}75$ in$.$ The ends A and $C$ are rigidly mounted to perfect magic physics walls that don't move or release the bar. What are the changes in lengths of sections $AB$ and $BC$ respectively?