Solution
= Solution
Power is transmitted at rate $P=C\Omega$, so
$$
C=\frac{4.0\times10^4}{300}\ \mathrm{N\,m}
=133.3\ \mathrm{N\,m}.
$$
For $a=0.040\ \mathrm m$, $L=3.0\ \mathrm m$ and $G=80\times10^9\ \mathrm{Pa}$, the <polar second moment of area> is $J_p=4.021\times10^{-6}\ \mathrm{m^4}$. Hence
$$
\boxed{\phi=\frac{CL}{GJ_p}
\simeq1.24\times10^{-3}\ \mathrm{rad}
=0.0712^\circ.}
$$
The density does not enter this static torsional deformation.