MHT CET · Physics · Rotational Motion

Four thin metal rods each of mass ' \(M\) ' and length ' \(L\) ', are welded end to end to form a square. The moment of inertia of the system about an axis passing through the centre of the square and perpendicular to its plane is

A \(\frac{\mathrm{ML}^2}{3}\)
B \(\frac{2 \mathrm{ML}^2}{3}\)
C \(\frac{2 \mathrm{ML}^2}{9}\)
D \(\frac{4 \mathrm{ML}^2}{3}\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(\frac{4 \mathrm{ML}^2}{3}\)

Step-by-step Solution

Detailed explanation

Moment of inertia of the system about an axis passing through O
\(\begin{aligned}
\mathrm{I}_0 & =4\left[\mathrm{MI} \text { of } \operatorname{rod}+\mathrm{m}\left(\frac{\mathrm{~L}}{2}\right)^2\right] \\
& =4\left[\frac{\mathrm{ML}^2}{12}+\frac{\mathrm{ML}^2}{4}\right] \\
& =\frac{4}{3} \mathrm{ML}^2
\end{aligned}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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