A single cylinder oil engine works with a three rotor system, the shaft length is 2.5m and 70mm in diameter, the middle rotor is at a distance 1.5m from one end. Calculate the free torsional vibration frequency for a single node system in Hz if the mass moment of inertia of rotors in Kg-m^2 are: 0.15, 0.3 and 0.09. C=84 kN/mm^2

(a) 171

(b) 181

(c) 191

(d) 201

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This intriguing question originated from Torsionally Equivalent Shaft topic in portion Torsional Vibrations of Machine Dynamics