NEET Sample Paper NEET Sample Test Paper-33

  • question_answer
    A solid sphere is rotating about a diameter at an angular velocity co. If it cools so that its radius reduces to \[\frac{1}{n}\]of its original value, its angular velocity becomes:                                  

    A)  \[\frac{\omega }{2n}\]

    B)  \[\frac{\omega }{{{n}^{2}}}\]

    C)  \[n\omega \]

    D)  \[{{n}^{2}}\omega \]

    Correct Answer: D

    Solution :

    In this case angular momentum remains conserved. According to law of conservation of angular momenutm, when no external torque is acting upon a body rotation about as axis then the angular  momentum of the body remains constant that is: \[J=I\omega .\] Where I is moment of Inertia and co the angular velocity Also,      \[I=\frac{2}{5}M{{R}^{2}}\] for a solid sphere Here,      \[{{R}_{1}}=R,\,{{R}_{2}}=\frac{R}{n}\] \[\therefore \] \[\frac{2}{5}M{{R}^{2}}{{\omega }_{1}}=\frac{2}{5}M{{\left( \frac{R}{n} \right)}^{2}}\times {{\omega }^{2}}\] \[\Rightarrow \] \[{{\omega }_{2}}={{n}^{2}}{{\omega }_{1}}.\] Here,  \[{{\omega }_{1}}=\omega ,\] therefore \[{{\omega }^{2}}={{n}^{2}}\omega \]


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