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Motion In Straight Line

Question
CBSEENPH11017800

At what height above the surface of the earth, the acceleration due to gravity will be of the same as in a mine, 100 km deep? 

Solution

Let, the acceleration due to gravity at height h be the same as that at a depth, d, deep into the earth. 
We have, d = 100 km 
Therefore, 
g' = g open parentheses 1 space minus fraction numerator 2 straight h over denominator straight R end fraction close parentheses space equals space straight g space open parentheses 1 space minus straight d over straight R close parentheses
rightwards double arrow space space space space space space space space fraction numerator 2 straight h over denominator straight R end fraction space equals space straight d over straight R

rightwards double arrow space space space space space space space space space space space space space straight h space equals space straight d over 2 space equals space 100 over 2 space equals space 50 space km space