Note: Assume a positive internal torque.

The polar moment of inertia of the solid brass rod must be computed in order to calculate the angle of twist in segment $\left(1\right)$:

${\mathrm{J}}_1=\frac{\mathrm{\pi }}{32}{(32 \mathrm{mm})}^4=102,944 {\mathrm{mm}}^4$