JEE Main & Advanced Physics Simple Harmonic Motion JEE PYQ-Simple Harmonic Motion

  • question_answer
    A particle undergoing simple harmonic motion has time dependent displacement given by \[x(t)=A\sin \frac{\pi t}{90}.\] The ratio of kinetic to potential energy of this particle at t = 210 s will be- [JEE Main 11-Jan-2019 Morning]

    A)  \[\frac{1}{9}\]             

    B)       2     

    C)  1                    

    D)      None of these

    Correct Answer: D

    Solution :

    [d] The maximum kinetic energy of the particle is \[\frac{1}{2}m({{A}^{2}}{{\omega }^{2}}).\]
    The potential energy of the particle at any time t is\[\frac{1}{2}m{{\omega }^{2}}{{x}^{2}}\]Using energy conservation                                                            
    \[\Rightarrow \]\[\frac{KE}{PE}=\frac{K{{E}_{\max }}}{PE}-1\]
    \[\Rightarrow \]\[\frac{KE}{PE}=\frac{\frac{1}{2}m{{A}^{2}}{{\omega }^{2}}}{\frac{1}{2}m{{\omega }^{2}}{{x}^{2}}}-1\]
    \[=\frac{{{A}^{2}}}{{{A}^{2}}{{\sin }^{2}}\frac{\pi }{90}\times 210}-1\]
    \[=\frac{1}{{{\left[ \sin \left( 2\pi +\frac{\pi }{3} \right) \right]}^{2}}}-1=\frac{1}{3}\]
    * None of the given options is correct.


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