Past exam of the physics B course of the University of Cambridge / 2018 / Paper 1 / Section C / C12 / a / Solution

Power is transmitted at rate $P=C\Omega$, soFor $a=0.040\mathrm{m}$, $L=3.0\mathrm{m}$ and $G=80\times 10^9\mathrm{Pa}$, the polar second moment of area is $J_p=4.021\times 10^{-6}{\mathrm{m}}^4$. HenceThe density does not enter this static torsional deformation.