BCECE Medical BCECE Medical Solved Papers-2006

  • question_answer
    The length of a simple pendulum is about 100cm known to an accuracy of 1mm. Its period of oscillation is 2s determined by measuring the time for 100 oscillations using a clock of 0.1 s resolution. What is the accuracy in the determined value of g?

    A)  0.2%          

    B)  0.5%

    C)  0.1%

    D)  2%

    Correct Answer: A

    Solution :

    Time period of a simple pendulum                 \[T=2\pi \sqrt{\frac{L}{g}}\] or            \[g=\frac{4{{\pi }^{2}}L}{{{T}^{2}}}\] .... (i) Differentiating Eq. (i), we have                 \[\frac{\Delta g}{g}+\frac{\Delta L}{L}+\frac{2\Delta T}{T}\] ?. (ii) Given,   \[L=100\,\,cm,\,\,T=2\,s\],                 \[\Delta T=\frac{0.1}{100}=0.001\,\,s\],                 \[\Delta L=1\,mm=0.1\,\,cm\] Substituting the values in Eq. (ii), we have                 \[\therefore \]    \[{{\left| \frac{\Delta g}{g} \right|}_{\max }}=\frac{\Delta L}{L}+\frac{2\Delta T}{T}=\frac{0.1}{100}+2\times \frac{0.001}{2}\] Thus, maximum percentage error \[{{\left| \frac{\Delta g}{g} \right|}_{\max }}\times 100=\left( \frac{0.1}{100}\times 100 \right)\] \[+\left( \frac{2\times 0.001}{2}\times 100 \right)\]


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