JEE Mains · Physics · STD 11 - System of particles and rotational motion
- JEE Mains 2021
- Hard
- Numerical
A uniform thin bar of mass \(6 \,kg\) and length \(2.4\, meter\) is bent to make an equilateral hexagon. The moment of inertia about an axis passing through the centre of mass and perpendicular to the plane of hexagon is ...... \(\times \,10^{-1} \,kg m ^{2}\)
Pick an option to check your answer.
Answer & Solution
Correct Answer
(B) \(8\)
Step-by-step Solution
Detailed explanation
\(6 \ell=2.4 \quad \ell=0.4 \,m\)
\(\sin 60^{\circ}=\frac{ r }{\ell}\)
\(r =\ell \sin 60^{\circ}=\frac{\ell \sqrt{3}}{2}\)
MOI, \(\quad I=\left[\frac{m \ell^{2}}{12}+\operatorname{mr}^{2}\right] 6\)
\(=\left[\frac{ m \ell^{2}}{12}+ m \left(\frac{\ell \sqrt{3}}{2}\right)^{2}\right] 6\)
\(=5 \,m l ^{2}\)
\(=5 \times 1 \times 0.16\)
\(=0.8\)
\(I=8 \times 10^{-1}\, kg m ^{2}\)
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