RAJASTHAN PMT Rajasthan - PMT Solved Paper-2005

  • question_answer
    The weight of an object at earths surface is 700 g wt. What will be its weight at the surface of a planet whose radius is ½ and mass is 1/7 of that of the earth?

    A)  200 g wt.                            

    B)  400 g wt.

    C)  50 g wt.              

    D)         300 g wt.

    Correct Answer: B

    Solution :

    Weight at earths surface w = mg Acceleration due to gravity at earths surface \[g=\frac{G{{M}_{e}}}{R\,_{e}^{2}}\] For planet, \[g=\frac{G{{M}_{e}}}{R{{\,}^{2}}}=\frac{G{{M}_{e}}/7}{{{({{R}_{e}}/2)}^{2}}}\]                                       \[=\frac{4}{7}\frac{G{{m}_{e}}}{R\,_{e}^{2}}=\frac{4}{7}g\]    \[\therefore \] Weight at the surface of planet=mg                                              \[=m\left( \frac{4g}{7} \right)\]                                     \[=\frac{4}{7}mg=\frac{4}{7}\times 700\]                                     \[=400\,g\,wt.\]


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