11th Class Physics Systems Of Particles & Rotational Motion / कणों के निकाय तथा घूर्णी गति Question Bank 11th CBSE Physics Rotational Motion

  • question_answer
    Two discs of same mass and thickness are made of materials having different densities. Which one of them will have larger moment of inertia?

    Answer:

     Here, \[{{m}_{1}}={{m}_{2}}\]                                   \[\therefore \]  \[{{V}_{1}}{{\rho }_{1}}={{V}_{2}}{{\rho }_{2}}\]                                                                                                 \[\left( \pi r_{1}^{2} \right)t.{{\rho }_{1}}=\left( \pi r_{2}^{2} \right)t{{\rho }_{2}}\]                                                                                                 \[\frac{{{\rho }_{1}}}{{{\rho }_{2}}}=\frac{r_{2}^{2}}{r_{1}^{2}}\]                                                               ??.. (i) Now,                                     \[\frac{{{I}_{1}}}{{{I}_{2}}}=\frac{\frac{1}{2}{{m}_{1}}r_{1}^{2}}{\frac{1}{2}{{m}_{2}}r_{2}^{2}}=\frac{r_{1}^{2}}{r_{2}^{2}}\]                                                \[\left( \because \,\,\,{{m}_{1}}={{m}_{2}} \right)\]                                                                 \[\frac{{{I}_{1}}}{{{I}_{2}}}=\frac{{{\rho }_{2}}}{{{\rho }_{1}}}\]                                                   ??? using (i) \[\therefore \]                                  \[I\propto \frac{1}{\rho }\] The disc of material with lower density will have larger moment of inertia.


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