NEETPhysicsRotational MotionMCQ+4 / −1
The moment of inertia of a thin rod about an axis passing through its mid point and perpendicular to the rod is . The length of the rod is nearly:
- A8.5 cm
- B17.5 cm
- C20.7 cm
- D72.0 cm
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Correct answer: A
$$ \begin{aligned} & \text { Moment of inertia of rod }=I=\frac{m \ell^2}{12} \\ & \Rightarrow \quad 2400=400 \frac{\ell^2}{12} \\ & \Rightarrow \quad 72=\ell^2 \\ & \Rightarrow \quad \ell=\sqrt{72}=8.48 \mathrm{~cm} \simeq 8.5 \mathrm{~cm} \end{aligned}$$
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