If distance between centres of Earth and Moon is D and mass of Earth is 81, times that of Moon. At w

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7.Gravitation

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If the distance between the centres of Earth and Moon is $D$ and mass of Earth is $81\, times$ that of Moon. At what distance from the centre of Earth gravitational field will be zero?

A

$\frac{D}{2}$

B

$\frac{2D}{3}$

C

$\frac{4D}{5}$

D

$\frac{9D}{10}$

Solution

let distance from earth's centre $=x$

Net gravitational field is zero

$\frac{\mathrm{G} \cdot 81 \mathrm{M}}{\mathrm{x}^{2}}=\frac{\mathrm{GM}}{(\mathrm{D}-\mathrm{x})^{2}}$

$\mathrm{x}=\frac{9}{10} \mathrm{D}$

Standard 11

Physics

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