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JEE Mains · Physics · STD 11 - Gravitation
  • JEE Mains 2020
  • Hard
  • MCQ

The value of the acceleration due to gravity is \(g _{1}\) at a height \(h =\frac{ R }{2}( R =\) radius of the earth) from the surface of the earth. It is again equal to \(g _{1}\) at a depth \(d\) below the surface of the earth. The ratio \(\left(\frac{ d }{ R }\right)\) equals

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Correct Answer

(D) \(\frac{5}{9}\)

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Detailed explanation

\(g_{1}=\frac{G M}{\left(R+\frac{R}{2}\right)^{2}} \ldots(1)\)

\(g_{2}=\frac{G M(R-d)}{R^{3}} \ldots(2)\)

\(g_{1}=g_{2}\)

\(\frac{G M}{\left(\frac{3 R}{2}\right)^{2}}=\frac{G M(R-d)}{R^{3}}\)

\(\Rightarrow \frac{4}{9}=\frac{( R - d )}{ R }\)

\(4 R=9 R-9 d\)

\(5 R =9 d \Rightarrow \frac{ d }{ R }=\frac{5}{9}\)

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