NEET 2022 Physics Radius of Gyration MCQ Question

Chapter: System of Particles and Rotational Motion Class: 11 Physics — Chapter 6 Topic: Radius of Gyration Difficulty: 🟡 Medium

✅ Ans: D — $\sqrt2:1$

Radius of gyration:

$$k=\sqrt{\frac{I}{M}}$$

For a disc about an axis normal to its plane:

$$I_1=\frac12MR^2$$ $$k_1=\frac{R}{\sqrt2}$$

About its diameter:

$$I_2=\frac14MR^2$$ $$k_2=\frac{R}{2}$$

Therefore,

$$\frac{k_1}{k_2} =\frac{R/\sqrt2}{R/2} =\sqrt2$$ $$\boxed{k_1:k_2=\sqrt2:1}$$

📌 Key formulas: Disc: $I_{\perp}=\frac12MR^2$, $I_{\text{diameter}}=\frac14MR^2$. (medicneet.com)

🧠 NEET Trick: For radius of gyration, take square root of $I/M$. Don't directly compare moments of inertia.