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Units And Measurement

Question
CBSEENPH11017701

Two satellites of equal masses are orbiting the earth in different radii such that time period of revolutions are T and 2T. What is the ratio of moment of inertia of two satellites about the centre of the earth respectively?

Solution
Let R1 and Rbe the radii of orbits of satellites having time period T and 2T. 
               

According to Kepler's third law, 

T2 ∝ R
space space space
therefore space space space space space space space open parentheses straight R subscript 1 over straight R subscript 2 close parentheses cubed equals open parentheses straight T subscript 1 over straight T subscript 2 close parentheses squared equals open parentheses fraction numerator straight T over denominator 2 straight T end fraction close parentheses squared equals 1 fourth

therefore space space space space space space space space open parentheses straight R subscript 1 over straight R subscript 2 close parentheses squared equals open parentheses 1 fourth close parentheses to the power of 2 divided by 3 end exponent equals open parentheses 1 half close parentheses to the power of 4 divided by 3 end exponent 


Ratio of the moment of inertia of first to second satellite is,
straight I subscript 1 over straight I subscript 2 equals mR subscript 1 squared over mR subscript 2 squared equals open parentheses straight R subscript 1 over straight R subscript 2 close parentheses squared equals open parentheses 1 half close parentheses to the power of 4 divided by 3 end exponent