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A circular disc D1of mass M and radius R has two identical discs D2 and D3 of the same mass M and radius R attached rigidly at its opposite ends (see figure). The moment of interia of the system about the axis OO', passing through the centre of D1, as shown in the figure, will be:

  • Option 1)

    3MR2

  • Option 2)

     

    \frac{2}{3}MR^{2}

  • Option 3)

     

    MR2

  • Option 4)

     

    \frac{4}{5}MR^{2}

Answers (1)

best_answer

 

Paraller Axis Theorem -

I_{b\: b'}=I_{a\: a'}+Mh^{2}

- wherein

b\: b' is axis parallel to a\: a' & a\: a' an axis passing through centre of mass.

 

 

I=I_{1}+I_{2}+I_{3}

I_{1}=M.O.I of D_{1} about {00}'

=\frac{MR^{2}}{2}

I_{2}=M.O.I of D_{3} about {00}'

I_{2}=I_{3}\Rightarrow due to symmetry

I_{2}=\left ( \frac{MR^{2}}{4} +MR^{2}\right )

I=I_{1}+2I_{2}

=\frac{MR^{2}}{2}+2\left ( \frac{MR^{2}}{4}+MR^{2} \right )

I=\frac{MR^{2}}{2}+2\times \frac{5MR^{2}}{4}

I=\frac{6MR^{2}}{2}

I=3MR^{2}

 

 


Option 1)

3MR2

Option 2)

 

\frac{2}{3}MR^{2}

Option 3)

 

MR2

Option 4)

 

\frac{4}{5}MR^{2}

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