NEET AIPMT SOLVED PAPER SCREENING 2005

  • question_answer
                    Imagine a new planet having the same density as that of earth but it is 3 times bigger than the earth in size. If the acceleration due to gravity on the surface of earth is g and that on the surface of the new planet is g', then:                                                                                                                                                                    

    A)                 \[g'=3\,g\]          

    B)                 \[g'=\frac{g}{9}\]             

    C)                 \[g'=9\,g\]          

    D)                 \[g'=27\,g\]

    Correct Answer: A

    Solution :

                    The acceleration due to gravity on the new planet can be found using the relation                 \[g=\frac{GM}{{{R}^{2}}}.....(i)\]                 but \[M=\frac{4}{3}\,\pi {{R}^{3}}\rho ,\,\rho \] being density                 Thus, Eq. (i) becomes                         \[\therefore g=\frac{G\times \frac{4}{3}\,\pi \,{{R}^{3}}\rho }{{{R}^{2}}}\]                 \[=G\times \frac{4}{3}\pi \,\,R\,\rho \]                         \[\Rightarrow \,R\,\,\propto \,\,R\]                         \[\therefore \frac{g'}{g}=\frac{R'}{R}\] \[\Rightarrow \frac{g'}{g}=\frac{3\,R}{R}=3\] \[\Rightarrow g'=3g\]


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