JEE Main & Advanced JEE Main Paper (Held On 10-Jan-2019 Evening)

  • question_answer
    A particle executes simple harmonic motion with an amplitude of 5 cm. When the particle is at 4 cm from the mean position, the magnitude of its velocity in SI units is equal to that of its acceleration. Then, its periodic time in seconds is- [JEE Main Online Paper (Held On 10-Jan-2019 Evening]

    A) \[\frac{4\pi }{3}\]                                  

    B) \[\frac{3\,}{8}\pi \]

    C) \[\frac{7\,}{3}\pi \]                    

    D)                  \[\frac{8\,\pi }{3}\]

    Correct Answer: D

    Solution :

    \[v=\omega \sqrt{{{A}^{2}}-{{x}^{2}}}\] \[a={{\omega }^{2}}x\] \[v=a\]                          (according to question \[\left| velocity \right|\text{ = }\left| acceleration \right|\text{ })\] \[~\omega \sqrt{{{A}^{2}}-{{x}^{2}}}\,=\,{{\omega }^{2}}x\] \[~\sqrt{{{A}^{2}}-{{x}^{2}}}\,=\,\omega x\] \[{{A}^{2}}-{{x}^{2}}={{\omega }^{2}}{{x}^{2}}\] \[25-16={{\omega }^{2}}\times 16\] \[9={{\omega }^{2}}\times 16\] \[\omega \,\,=\,\,\sqrt{\frac{9}{16}}\,\,=\,\frac{3}{4}\] \[T\,\,=\,\,\frac{2\pi }{\omega }\,=\,\frac{2\pi }{3}\,\times 4\,\,=\,\,\frac{8\,\pi }{3}\,\sec \]


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