NEET AIPMT SOLVED PAPER SCREENING 2008

  • question_answer
    A point performs simple harmonic oscillation of period T and the equation of motion is given by \[x=c\sin (\omega t+\pi /6).\] After the elapse of what fraction of the time period the velocity of the point will be equal to half of its maximum velocity?

    A) \[\frac{T}{8}\]   

    B)                        \[\frac{T}{6}\]

    C) \[\frac{T}{3}\]                                   

    D) \[\frac{T}{12}\]

    Correct Answer: D

    Solution :

    Key Idea: Velocity is the time derivative of displacement. Writing .the given equation of a point performing SHM\[x=a\sin \left( \omega t+\frac{\pi }{6} \right)\]  ...(i) Differentiating Eq. (i), w.r.t. time, we obtain \[v=\frac{dx}{dt}=a\,\omega \cos \left( \omega t+\frac{\pi }{6} \right)\] It is given that \[v=\frac{a\omega }{2},\]so that \[\frac{a\omega }{2}=a\omega \cos \left( \omega t+\frac{\pi }{6} \right)\]or\[\frac{1}{2}=\cos \left( \omega t+\frac{\pi }{6} \right)\] or\[\cos \frac{\pi }{3}=\cos \left( \omega t+\frac{\pi }{6} \right)\]or\[\omega t+\frac{\pi }{6}=\frac{\pi }{3}\] \[\Rightarrow \]\[\omega t=\frac{\pi }{6}\]or\[t=\frac{\pi }{6\omega }=\frac{\pi \times T}{6\times 2\pi }=\frac{T}{12}\] Thus, at\[\frac{T}{12}\]velocity of the point will be equal to half of its maximum velocity.


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