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A uniform thin rod of length  4l, mass 4m is bent at the points as shown in the figure. What is the moment of inertia of the rod about the axis passing through point O & perpendicular to the plane of the paper.

Option: 1

\frac{m\: l^{2}}{3}


Option: 2

\frac{10m\: l^{2}}{3}


Option: 3

\frac{m\: l^{2}}{12}


Option: 4

\frac{m\: l^{2}}{24}


Answers (1)

best_answer

Moment of inertia of uniform rod of length(l) -

I= \frac{Ml^{2}}{12}

About axis passing through its centre & perpendicular to its length.

  The given structure can be broken into 4 parts

For AB:I=I_{CM}+m\times d^{2}=\; \frac{ml^{2}}{12}+\frac{5m}{4}l^{2}\; ;\; I_{AB}=\frac{4}{3}ml^{2}

                           

For BO : I=\frac{ml^2}{3}

For composite frame : (by symmetry)

I=2\left [ I_{AB}+I_{OB} \right ]=2\left [ \frac{4ml^{2}}{3}+\frac{ml^{2}}{3} \right ]=\frac{10}{3}ml^{2}.

 

 

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Gunjita

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