JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Morning)

  • 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 Online Paper (Held On 11-Jan-2019 Morning]

    A) \[\frac{1}{9}\]                                      

    B) 2     

    C) 1                     

    D)                  3

    E)                  None of these

    Correct Answer: E

    Solution :

    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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