A cylindrical rod of steel $(E=207 \mathrm{GPa}, 30 \times$ $\left.10^{6} \text { psi }\right)$ having a yield strength of $310 \mathrm{MPa}$ $(45,000 \mathrm{psi})$ is to be subjected to a load of $11,100 \mathrm{N}\left(2500 \mathrm{lb}_{\mathrm{f}}\right) .$ If the length of the rod is $500 \mathrm{mm}(20.0 \text { in. }),$ what must be the diameter to allow an elongation of $0.38 \mathrm{mm}(0.015 \text { in. }) ?$