The figure shows two rotors connected by an elastic shaft undergoing torsional vibration. The rotor A has a mass of 2 kg and a diameter of 60 cm, while the rotor B has a mass of 1 kg and a diameter of 20 cm. What is the distance L at which the node of vibration of torsional vibration occurs?

• A. 36 cm
• B. 30 cm
• C. 22 cm
• D. 18 cm