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NEET Physics Gravitation 2026 NEET 2026 (Re-NEET)

NEET Physics Question (2026) — Solution

Question

In a solar system, the time-period of revolution of a planet tracing a circular orbit of radius R is proportional to :

Options

  1. A. R ^3
  2. B. R ^ 1/2
  3. C. R ^ 3/2
  4. D. R ^2

Answer

C. R ^ 3/2

Step-by-step solution

According to Kepler's third law of planetary motion, the square of the time period of revolution of a planet around the sun is directly proportional to the cube of the semi-major axis of its elliptical orbit. For a circular orbit, the semi-major axis is equal to the radius of the orbit R. Therefore, T^2 R^3 Taking the square root on both sides, we get: T R^ 3/2 Alternatively, equating the gravitational force to the required centripetal force: GMm R^2 = mv^2 R v = GM R The time period T is given by: T = 2 R v = 2 R GM R = 2 GM R^ 3/2 Thus, T R^ 3/2 . Answer: R ^ 3/2

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