Determine the relationship between the torque N and the torsion angle for (a) The tube whose wall thickness hr is considerably less than the tube

Determine the relationship between the torque N and the torsion angle φ for
(a) The tube whose wall thickness hr is considerably less than the tube radius;
(b) For the solid rod of circular cross-section. Their length l, radius r, and shear modulus G are supposed to be known