Manipal Engineering Manipal Engineering Solved Paper-2013

  • question_answer
    The speed with which the earth have to rotate on its axis so that a person on the equator would weight\[{{(3/5)}^{th}}\]as much as present. [Radius of earth = 6400 km]

    A) \[4.83\times {{10}^{-3}}rad{{s}^{-1}}\]

    B) \[5.41\times {{10}^{-3}}rad{{s}^{-1}}\]

    C) \[7.82\times {{10}^{-4}}rad{{s}^{-1}}\]

    D) \[8.88\times {{10}^{-14}}rad{{s}^{-1}}\]

    Correct Answer: C

    Solution :

    The apparent weight of person on the equator (latitude\[\lambda =0\]) is given by                 \[\omega =W-mR{{\omega }^{2}}\] Here,     \[\omega =(3/5)w=(3/5)mg\]    \[[\because \,\,\omega =mg]\] or            \[mR{{\omega }^{2}}=mg-(3/5)mg=\left( \frac{2}{5} \right)mg\] or            \[{{\omega }^{2}}=\frac{2g}{5R}\]                 \[\omega =\sqrt{\frac{2g}{5R}}\] Here,     \[g=9.8m{{s}^{-2}}\] and        \[R=6400km=6400\times {{10}^{3}}m\] \[\therefore \]  \[\omega =\sqrt{\left( \frac{2}{5}\times \frac{9.8}{6400\times {{10}^{3}}} \right)}rad{{s}^{-1}}\]                 \[=7.82\,\times {{10}^{-4\,}}\,rad{{s}^{-1}}\]


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