$4\mathrm{.}24$ A $\backslash (60-\backslash$mathrm$\{$N$\}\backslash$cdot $\backslash$mathrm$\{$m$\}\backslash )$ couple is applied to the steel bar shown. $($a$)$ Assuming that the couple is applied about the $\backslash ($ z $\backslash )$ axis as shown, determine the maximum stress and the radius of curvature of the bar. $($b$)$ Solve part $\backslash ($ a $\backslash ),$ assuming that the couple is applied about the $\backslash ($ y $\backslash )$ axis. Use $\backslash ($ E$=200\backslash$mathrm$\{$GPa$\}\backslash ).$

Fig. P$4\mathrm{.}24$