BHU PMT BHU PMT (Mains) Solved Paper-2011

  • question_answer
    The speed of earth's rotation about its axis is co. Its speed increases to\[x\]times to make effective acceleration due to gravity equal to zero at the equator,\[x\]is

    A)  1                                            

    B)  8.5

    C)  17                                         

    D)  34

    Correct Answer: C

    Solution :

                      Acceleration due to gravity at equator \[g'=g-{{R}_{c}}{{\omega }^{2}}\] \[\therefore \]  \[0=g-{{R}_{e}}{{(x\omega )}^{2}}\] \[\Rightarrow \]               \[g={{R}_{e}}{{x}^{2}}{{\omega }^{2}}\] \[\Rightarrow \]               \[x=\sqrt{\frac{g}{{{R}_{e}}{{\omega }^{2}}}}=\frac{1}{\omega }\sqrt{\frac{g}{{{R}_{e}}}}\]                 \[=\frac{1}{\frac{2\pi }{24\times 60\times 60}}\sqrt{\frac{10}{6400\times {{10}^{3}}}}\]                 \[=\frac{24\times 60\times 60}{2\pi }.\frac{1}{800}\]                 \[=17\]


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