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Motion In Straight Line

Question
CBSEENPH11020669

A particle of mass m is thrown upwards from the surface of the earth, with a velocity u. The mass and the radius of the earth are, respectively, M and R.G are gravitational constant and g is acceleration due to gravity on the surface of the earth. The minimum value of u so that the particle does not return back to earth is 

  • square root of fraction numerator 2 GM over denominator 2 end fraction end root
  • square root of fraction numerator 2 GM over denominator straight R squared end fraction end root
  • square root of 2 gR squared end root
  • square root of fraction numerator 2 GM over denominator straight R squared end fraction end root

Solution

A.

square root of fraction numerator 2 GM over denominator 2 end fraction end root straight v subscript straight e space equals space square root of 2 gR end root

straight v subscript straight e space equals space square root of fraction numerator 2 GM over denominator straight R squared end fraction straight x space straight R end root space space left parenthesis therefore space GM space equals space gR squared right parenthesis

straight v subscript straight e space equals space square root of fraction numerator 2 GM over denominator straight R end fraction end root