If two gears have moment of inertias as $I_1$ and $I_2$ respectively and mesh with a speed ratio $\omega_2/\omega_1 = n$, then equivalent moment of inertia of both gears referred to first one is
- A. $n² I_1 + I_2$
- B. $I_1 + n I_2$
- C. $n I_1 + I_2$
- D. $I_1 + n² I_2$
Answer: D. $I_1 + n² I_2$
Explanation: Kinetic energy equivalence: $\frac{1}{2} I_{eq} \omega_1^2 = \frac{1}{2} I_1 \omega_1^2 + \frac{1}{2} I_2 \omega_2^2$. Since $\omega_2 = n \omega_1$, $I_{eq} = I_1 + n² I_2$.