JEE Main & Advanced Physics Rotational Motion JEE PYQ-Rotational Motion

  • question_answer
    A particle performing uniform circular motion has angular momentum L. If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is                                                [AIEEE 2003]

    A)   \[\frac{L}{4}\]                        

    B)   2L   

    C)   4L                 

    D)   \[\frac{L}{2}\]

    Correct Answer: A

    Solution :

    [a] Angular momentum
    \[L=\operatorname{l}\omega \]                                   ... (i)
    Kinetic energy \[K=\frac{1}{2}l{{\omega }^{2}}=\frac{1}{2}L\omega \] [from Eq. (i)]
    \[\therefore \]      \[L=\frac{2K}{\omega }\]
    Now, the new angular momentum
    \[L'=\frac{2\left( \frac{K}{2} \right)}{2\omega }\]  \[\left( \because K'=\frac{K}{2}and\omega '=2\omega  \right)\]
    \[\Rightarrow \]   \[L'=\frac{L}{4}\]


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