9th Class Science Gravitation and Floatation Question Bank Gravitation

  • question_answer
    The escape velocity from the earth's surface is 11 km/sec. A certain planet has a radius twice that of the earth but its mean density is the same as that of the earth. The value of the escape velocity from this planet would be

    A)  11 km/sec         

    B)  22 km/sec  

    C)  33 km/sec       

    D)         16.5 km/sec

    Correct Answer: B

    Solution :

     Escape velocity,\[{{v}_{e}}=\sqrt{\frac{2GM}{R}}\] where, \[M=\frac{4}{3}\pi {{4}^{3}}d\] \[\therefore \]  \[{{v}_{e}}=\sqrt{\frac{2G\times \frac{4}{3}\pi {{R}^{3}}d}{R}}\]                 \[{{v}_{e}}=\sqrt{\frac{8\pi {{R}^{2}}d}{3}}\] \[\Rightarrow \]               \[{{v}_{e}}\propto R\] Now,     \[\frac{{{({{v}_{e}})}_{earth}}}{{{({{v}_{e}})}_{planet}}}=\frac{{{R}_{earth}}}{{{R}_{planet}}}\]


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