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MHT CET 2020 (16 Oct, Shift 1) · Gravitational Field

Gravitational Field question from MHT CET 2020 (16 Oct, Shift 1)

Q8MHT CET 2020 · 16 OCT · SHIFT 1Medium

Gravitational Field

The mass of earth is 81 times the mass of the moon and the distance between their centres is RR. The distance from the centre of the earth, where gravitational force will be zero is

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Answer: (c)

81MME = 0x = 9R/10R/10
  1. At the null point the pulls of earth and moon are equal: GMex2=GMm(R−x)2\frac{GM_e}{x^2} = \frac{GM_m}{(R-x)^2}, with xx from the earth's centre.
  2. xR−x=MeMm=81=9\frac{x}{R-x} = \sqrt{\frac{M_e}{M_m}} = \sqrt{81} = 9
  3. x=9R−9x⇒x=9R10x = 9R - 9x \Rightarrow x = \frac{9R}{10}
  4. So the answer is (c) 9R10\frac{9R}{10}.
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