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JEE Main 2003 (AIEEE) · Newton's Law of Gravitation

Newton's Law of Gravitation question from JEE Main 2003 (AIEEE)

Q24JEE Main 2003 · AIEEEDifficult

Newton's Law of Gravitation

Two spherical bodies of mass MM and 5M5M & radii RR & 2R2R respectively are released in free space with initial separation between their centers equal to 12R12R. If they attract each other due to gravitational force only, then the distance covered by the smaller body just before collision is

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Answer: (c)

  1. Only internal forces act, so the centre of mass stays fixed.
  2. They collide when the centres are R+2R=3RR + 2R = 3R apart, so together they move 12R−3R=9R12R - 3R = 9R.
  3. Distances are inversely proportional to masses: x1x2=5MM=5\frac{x_1}{x_2} = \frac{5M}{M} = 5.
  4. x1=56×9R=7.5Rx_1 = \frac{5}{6} \times 9R = 7.5R
  5. So the answer is (c) 7.5R7.5R.
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