BHU PMT BHU PMT Solved Paper-2001

  • question_answer
    The displacement of the particle from its mean Position (in meter) varies with time (in second) According to the equation: \[y=0.2\,\,\sin \,\,\left( 10\pi t+1.5\pi  \right)\cos \left( 10\pi t+1.5\pi  \right)\]. The motion of the particle is:

    A)  Along a circular path

    B)  Simple harmonic motion with time period 0.1 s

    C)  No simple harmonic motion

    D)  Simple harmonic motion with time period 0.2 s

    Correct Answer: B

    Solution :

    The displacement equation is given by \[y=0.2\,\sin \left( 10\pi \,t+1.5\pi  \right)\,\cos \,\left( 10\,\pi \,t+1.5\pi  \right)\] Rearranging the terms, we have \[y=0.1\left[ 2\,\sin \,\left( 10\,\pi t+1.5\,\pi  \right)\cos \,\left( 10\,\pi t+1.5\pi  \right) \right]\] Using 2 sin A cos A = sin 2 A, we have      \[y=0.1\,\,\sin \left( 20\,\pi \,t+3\pi  \right)\]                     ?(1) This equation takes the form of displacement equation in SHM, we have \[y=a\,\sin \left( \omega \,t+\phi  \right)\]                          ?(2) Where a is amplitude, \[\omega \] is angular velocity, \[\phi \] is phase difference. Comparing Eqs. (1)  and   (2), we get                                                 \[\omega t=20\,\pi \,t\] \[\Rightarrow \]                               \[\omega =20\,\pi \] Also time-period=\[\frac{2\pi }{\omega }=\frac{2\,\pi }{20\,\pi }=0.1\,s\]


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