Question

Two cylinders (one hollow, one solid) made of linear elastic materials with the same outer diameter and length are subjected to the same external torque. Neither cylinder breaks at this torque. Which cylinder has the greater twist angle at this torque?

Answer 1

The hollow cylinder, because this has greater inertia, due to the distance of the mass from its center. Studying this solids in revolution, you will find that inertia is an important part here, because it change speed and resistance of this objects.