RAJASTHAN PMT Rajasthan - PMT Solved Paper-2004

  • question_answer
    A spaceship of weight 39200 kg-W lands on planet mars whose radius is \[3.4\times {{10}^{6}}m\] and mass is \[6.42\,\times {{10}^{23}}kg\]. The weight of space ship on mars will be (surface   tension   of   water \[=7\times {{10}^{-2}}N/m\]):

    A)  5000 kg-W                         

    B)  10000 kg-W

    C)  15000 kg-W       

    D)         20000 kg-W

    Correct Answer: C

    Solution :

    The mass of spaceship \[m=\frac{39200}{9.8}=4000\,kg\] On earth, \[\frac{GMm}{{{R}^{2}}}\]                                       ...(i) On mars, \[g=\frac{GMm}{{{R}^{2}}}\]                   ?(ii) \[\therefore \]  \[\frac{g}{g}=\frac{M}{M}\times \frac{{{R}^{2}}}{R{{}_{2}}}\]                      ?(iii) Here: \[R=6400\,km=6.4\,\times {{10}^{6}}\,m,\]                 \[R=3.4\,\times {{10}^{6}}m\] \[M=6.0\times {{10}^{24}}\,kg,\,M=6.42\,\times {{10}^{23}}\,kg\] Putting the given values m eq (i) \[\therefore \]     \[g=\frac{6.42\times {{10}^{23}}\times {{(6.4\times {{10}^{6}})}^{2}}}{6\times {{10}^{24}}\times {{(3.4\times {{10}^{6}})}^{2}}}\times 9.8\] \[\Rightarrow \]              \[g\approx 3.7\,m/{{\sec }^{2}}\] Hence, the weight of spaceship on mars \[w=mg\] \[=4000\times 3.7\]  \[=14800\,\approx 15000\,kg\]


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