3. A heavy disk of mass moment of inertia ] is attached at the middle of a circular shaft of length I and diameter d as shown in figure below. By modeling the system as a single-degree-of-freedom torsional system, determine the undamped natural frequency (w) of torsional vibration. [Hint: the elasticity of two shaft sections can be modeled as two parallel torsional springs] Shaft, length dia.d Fixed Shaft, length dia Fixed