9th Class Science Gravitation and Floatation Question Bank Gravitation

  • question_answer
    A spaceship is launched into a circular orbit close to earth's surface. What additional velocity ha now to be imparted to the spaceship in the orbit to overcome the gravitational pull? (Radius of earth = 6400 km and\[\text{g }=\text{ 9}\text{.8 m}/{{\text{s}}^{\text{2}}}\])

    A)  2.83 km/s        

    B)         3.28 km/sec  

    C)  6.68 km/s       

    D)         8.32 km/sec      

    Correct Answer: B

    Solution :

     Orbital velocity of space-ship,             \[{{v}_{0}}=\sqrt{\frac{GM}{r}}\]                  \[(\because \,\,r>>R)\] Since\[,\]             \[g=\sqrt{\frac{GM}{{{R}^{2}}}}\], \[\therefore \]       \[GM=g{{R}^{2}}\] Now,     \[{{v}_{0}}=\sqrt{Rg}=\sqrt{6.4\times {{10}^{6}}\times 9.8}\]                     \[=7.9195\,\,km/s\] Again,   \[{{v}_{e}}=\sqrt{2rg}=\sqrt{2\times 7.9195}\]                     \[=11.20\,\,km/s\] \[\therefore \]Additional velocity required \[=11.20-7.9195\]                    \[=\mathbf{3}\mathbf{.28}\,\,\mathbf{km/sec}\]


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