• # question_answer A shaft has two heavy rotors mounted on it. The transverse natural frequencies, considering each of the rotor separately, are 100 cycles/sec and 200 cycles/sec respectively. The lowest critical speed is: A) 5367 rpm                      B) 6000 rpmC) 9360 rpm                      D) 12,000 rpm

$\frac{1}{f_{n}^{2}}=\frac{1}{f_{1}^{2}}+\frac{1}{f_{2}^{2}}$ $\frac{1}{{{100}^{2}}}+\frac{1}{{{200}^{2}}}=\frac{5}{{{200}^{2}}}$ $f_{n}^{2}=\frac{{{200}^{2}}}{5},$ ${{f}_{n}}=5367\,\,rpm$