A thin$-$walled steel tube having an elliptical cross section with constant thickness $t($see Fig.

Q$4)$ is subjected to a torque $T=2\mathrm{.}0kNm($values of the relevant parameters are:

$a=75mm,b=50mm,t=5mm,G=82$GPa

Determine the shear stress $$ and the rate of twist $($in degrees per $m)$

$($Problem $3\mathrm{.}11-7$ of Goodno & Gere, $9$e$,$ units changed to SI$)$

Fig. Q$4$