A shaft has two heavy rotors mounted on it. The transverse natural frequency considering each rotor separately is 100 hz & 200 hz respectively. The lowest critical speed is
- A. 13000 rpm
- B. 5367 rpm
- C. 6450 rpm
- D. 9343 rpm
Answer: B. 5367 rpm
Explanation: Dunkerley's Formula: 1/f² = 1/f1^2 + 1/f2^2. 1/f² = 1/100^2 + 1/200^2 = 5/40000. f = $\sqrt{8000}$ = 89.44 Hz. N = 60f = 5366.4 rpm.