JEE Main & Advanced Physics Simple Harmonic Motion Question Bank Mock Test - Simple Harmonic Motion

  • question_answer
    Initially cylindrical drums \[P\] and \[Q\] were placed at equal distance \[L\] from center of mass \[C\] of the rough rod \[AB\] in horizontal position. The drums were spinning in opposite directions with angular velocities. The rod is displaced by distance \[x\] towards left and released so that it performs SHM. If difference in reactions at \[Q\] and \[P\] is \[\frac{mgx}{L}\] where m is the mass of the rod, find the time period of oscillations, if m is the coefficient of friction:

    A) \[2\pi \sqrt{\frac{L}{g}}\]          

    B) \[2\pi \sqrt{\frac{(L-x)}{g}}\]

    C) \[2\pi \sqrt{\frac{(L+x)}{\mu g}}\]         

    D) \[2\pi \sqrt{\frac{L}{\mu g}}\]

    Correct Answer: D

    Solution :

    [d] \[{{R}_{Q}}-{{R}_{P}}=\frac{mgx}{L}\] Frictional force at Q will be more than frictional force at P, and it will bring back the rod. Restoring force. \[F=-({{f}_{Q}}-{{f}_{p}})=-\mu ({{R}_{Q}}-{{R}_{P}})=-\frac{\mu mgx}{L}\] So \[K=\frac{\mu mg}{L};T=2\pi {{\left( \frac{m}{K} \right)}^{1/2}}=2\pi \sqrt{\frac{L}{\mu g}}\]


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