Two heavy rotating masses are connected by shafts of lengths $l_1, l_2$ and $l_3$ and the corresponding diameters are $d_1, d_2$ and $d_3$. This system is reduced to a torsionally equivalent length of the shafts is
- A. $l_1 + l_2 (d_1/d_2)^4 + l_3 (d_1/d_3)^4$
- B. $l_1 + l_2 (d_1/d_2)^3 + l_3 (d_1/d_3)^3$
- C. $(l_1+l_2+l_3)/3$
- D. $l_1+l_2+l_3$
Answer: A. $l_1 + l_2 (d_1/d_2)^4 + l_3 (d_1/d_3)^4$
Explanation: For equivalent stiffness, $L_e/d_e^4 = \sum L_i/d_i^4$. Assuming $d_e = d_1$, $L_e = L_1 + L_2(d_1/d_2)^4 + ...$