JEE Main & Advanced JEE Main Paper (Held On 15 April 2018) Slot-II

  • question_answer
    A think rod\[MN\], free to rotate in the vertical plane about the fixed end\[N\], is held horizontal. When the end \[M\] is released the speed of this end, when the rod makes an angle \[\alpha \] with the horizontal, will be proportional to: (see figure)                                                       [JEE Online 15-04-2018 (II)]

    A)                     \[\sqrt{\cos \alpha }\]                   

    B) \[\cos \alpha \]

    C) \[\sin \alpha \] 

    D)          \[\sqrt{\sin \alpha }\]

    Correct Answer: A

    Solution :

    When the rod makes an angle of \[\alpha \] displacement of centre of mass \[=\frac{l}{2}\cos \alpha \] \[mg\frac{l}{2}\cos \alpha =\frac{1}{2}l{{\omega }^{2}}\] \[mg\frac{l}{2}\cos \alpha =\frac{m{{l}^{2}}}{6}{{\omega }^{2}}\] \[\omega =\sqrt{\frac{3g\cos \alpha }{l}}\] speed of end \[=\omega \times l=\sqrt{3g\cos \alpha l}\] hence \[\omega \] is proportional to\[\sqrt{\cos \alpha }\]


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