Q. A particle of mass $m$ lies at a distance $r$ from the centre of earth. The force of attraction between the particle and earth as a function of distance is $F(r)$,

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A

$F(r) \propto \frac{1}{r^{2}}$ for $r< R$

B

$F(r) \propto \frac{1}{r^{2}}$ for $r \geq R$

C

$F(r) \propto r$ for $r< R$

D

$F(r) \propto \frac{1}{r}$ for $r< R$

Solution:

Outside the earth surface, as $g$ varies inversely proportional to square of the distance from center of earth option (A) is correct and inside the earth as $g$ varies as directly proportional to the distance option (C) is correct.

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