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Motion In Straight Line

Question
CBSEENPH11020290

What is the minimum energy required to launch a satellite of mass m from the surface of a planet of mass M and radius R in a circular orbit at an altitude of 2R?

  • 5GmM/6R

  • 2GmM/3R

  • GmM/2R

  • GmM/3R

Solution

A.

5GmM/6R

From conservation of energy,
Total energy at the planet = Total energy at the altitude
negative GMm over straight R space plus space left parenthesis KE right parenthesis subscript surface space equals space minus fraction numerator GMm over denominator 3 straight R end fraction space plus space 1 half mv subscript straight A superscript 2 space... space left parenthesis straight i right parenthesis
In its orbit the necessary centripetal force provided by gravitational force.
∴ therefore space fraction numerator mv subscript straight A superscript 2 over denominator left parenthesis straight R space plus 2 straight R right parenthesis end fraction space equals space fraction numerator GMm over denominator left parenthesis straight R space plus 2 straight R right parenthesis squared end fraction
straight v subscript straight A superscript 2 space equals space fraction numerator GM over denominator 3 straight R end fraction space... space left parenthesis ii right parenthesis
From space eq space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis space we space get
left parenthesis KE right parenthesis subscript surface space equals space 5 over 6 GMm over straight R