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JEE Mains · Physics · STD 11 - System of particles and rotational motion
- JEE Mains 2013
- Hard
- MCQ
A ring of mass \(M\) and radius \(R\) is rotating about its axis with angular velocity \(\omega \). Two identical bodies each of mass \(m\) are now gently attached at the two ends of a diameter of the ring. Because of this, the kinetic energy loss will be
Pick an option to check your answer.
Answer & Solution
Correct Answer
(C) \(\frac{{Mm}}{{\left( {M + 2m} \right)}}\,{\omega ^2}{R^2}\)
Step-by-step Solution
Detailed explanation
\(\begin{array}{l}
Kinetic\,energ{y_{\left( {rotational} \right)}}{K_R} = \frac{1}{2}I{\omega ^2}\\
kinetic\,energ{y_{(translational)}}{K_r} = \frac{1}{2}M{v^2}\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( {v = R\omega } \right)\\
M.{\mathop{\rm I}\nolimits} {._{(initial)}}{I_{ring}} = M{R^2};{\omega _{initial}} = \omega \\
M.I{._{\left( {new} \right)}}I{'_{\left( {system} \right)}} = M{R^2} + 2m{R^2}\\
\omega {'_{\left( {system} \right)}} = \frac{{m\omega }}{{M + 2m}}
\end{array}\)
Kinetic\,energ{y_{\left( {rotational} \right)}}{K_R} = \frac{1}{2}I{\omega ^2}\\
kinetic\,energ{y_{(translational)}}{K_r} = \frac{1}{2}M{v^2}\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( {v = R\omega } \right)\\
M.{\mathop{\rm I}\nolimits} {._{(initial)}}{I_{ring}} = M{R^2};{\omega _{initial}} = \omega \\
M.I{._{\left( {new} \right)}}I{'_{\left( {system} \right)}} = M{R^2} + 2m{R^2}\\
\omega {'_{\left( {system} \right)}} = \frac{{m\omega }}{{M + 2m}}
\end{array}\)
Solving we get loss in \(K.E.\)
\( = \frac{{Mm }}{{\left( {M + 2m} \right)}}{\omega ^2}{R^2}\)
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