$3-13.$ A bar having a length of $5$ in $.$ and cross$-$sectional

area of $0\mathrm{.}7in.{?}^2$ is subjected to an axial force of $8000$ lb $.$ If the

bar stretches $0\mathrm{.}002$ in$.,$ determine the modulus of elasticity

of the material. The material has linear$-$elastic behavior.