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

  • question_answer
    A damped harmonic oscillator has a frequency of 5 oscillations per second. The amplitude drops to half its value for every 10 oscillations. The time it will take to drop to \[\frac{1}{1000}\]of the original amplitude is close to: [JEE Main 8-4-2019 Afternoon]

    A)  100 s   

    B)       20 s

    C)  10 s                

    D)       50 s

    Correct Answer: B

    Solution :

    [b] \[A={{A}_{0}}{{e}^{-\gamma t}}\]
    \[A=\frac{{{A}_{0}}}{2}\]after 10 oscillations
    \[\because \]After 2 seconds
    \[\frac{{{A}_{0}}}{2}={{A}_{0}}{{e}^{-\gamma }}^{(2)}\]
    \[2={{e}^{2\gamma }}\]
    \[\ell n2=2\gamma \]
    \[\gamma =\frac{\ell n2}{2}\]
    \[\because \]\[A={{A}_{0}}{{e}^{-\gamma t}}\]
    \[\ell n\frac{{{A}_{0}}}{A}=\gamma t\]
    \[\ell n1000=\frac{\ell n2}{2}t\]
    \[2\left( \frac{3\ell n10}{\ell n2} \right)=t\]
    \[\frac{6\ell n10}{\ell n2}=t\]
    \[t=19.931\sec \]
    \[t\approx 20\sec \]


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