MHT CET · Physics · Rotational Motion

A thin metal wire of length ‘ $L$ ’ and uniform linear mass density ‘ $Q$ ’ is bent into a circular coil with ‘ $O$ ’ as centre. The moment of inertia of a coil about the axis $X X'$ is

A $3 Q L^{3} / 8 π^{2}$
B $Q L^{3} / 4 π^{2}$
C $3 Q L^{2} / 4 π^{2}$
D $Q L^{3} / 8 π^{2}$

Verified Solution

Answer & Solution

Correct Answer

(A) $3 Q L^{3} / 8 π^{2}$

Step-by-step Solution

Detailed explanation

I_{x x'} = \frac{m R^{2}}{2} + m R^{2}

= \frac{3}{2} . m R^{2}

∴ 2 π R = L ∴ R = \frac{L}{2 π}

I_{x x'} = \frac{3}{2} (Q) . 2 π R . R^{2}

= 3 Q π (R^{3})

= \frac{3 Q π . L^{3}}{8 π^{3}}

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.

Same subject

Explore more questions on app

From MHT CET

Explore more questions on app

A thin metal wire of length ‘ L ’ and uniform linear mass density ‘ Q ’ is bent into a circular coil with ‘ O ’ as centre. The moment of inertia of a coil about the axis XX' is

Step-by-step Solution

A thin metal wire of length ‘ $L$ ’ and uniform linear mass density ‘ $Q$ ’ is bent into a circular coil with ‘ $O$ ’ as centre. The moment of inertia of a coil about the axis $X X'$ is