किसी ठोस गोले का द्रव्यमान \(M\) तथा इसकी त्रिज्या \(R\) है। इसमें से अधिकतम संभव आयतन का एक क्यूब (घन) काट लिया जाता है। इस क्यूब का जड़त्व आघूर्ण कितना होगा, यदि, इसकी घूर्णन-अक्ष, इसके केन्द्र से होकर गुज़रती है तथा इसके किसी एक फलक के लम्बवत् है ?

A \(\frac{{M{R^2}}}{{16\sqrt 2 \pi }}\)
B \(\frac{{4M{R^2}}}{{9\sqrt 3 \pi }}\)
C \(\;\frac{{4M{R^2}}}{{3\sqrt 3 \pi }}\)
D \(\;\frac{{M{R^2}}}{{32\sqrt 2 \pi }}\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(\frac{{4M{R^2}}}{{9\sqrt 3 \pi }}\)

Step-by-step Solution

Detailed explanation

\(\begin{array}{l} Here\,a = \frac{2}{{\sqrt 3 }}R\\ Now,\frac{M}{{M'}} = \frac{{\frac{4}{3}\pi {R^3}}}{{{a^3}}}\\ = \frac{{\frac{4}{3}\pi {R^3}}}{{{{\left( {\frac{2}{{\sqrt 3 }}R} \right)}^3}}} = \frac{{\sqrt 3 }}{2}\pi .\,M' = \frac{{2M}}{{\sqrt 3 \pi }} \end{array}\) Moment…

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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