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JEE Main 2021 (1 Sep, Shift 2) · Satellites - Orbital Velocity & Period

Satellites - Orbital Velocity & Period question from JEE Main 2021 (1 Sep, Shift 2)

Q55JEE Main 2021 · 1 SEP · SHIFT 2Difficult

Satellites - Orbital Velocity & Period

Four particles each of mass M, move along a circle of radius R under the action of their mutual gravitational attraction as shown in figure. The speed of each particle is:

Figure

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Answer: (b)

F1F1F2Mcentre
  1. Adjacent masses: distance 2R\sqrt{2}R; opposite mass: distance 2R2R.
  2. Two adjacent pulls F1=GM22R2F_1 = \frac{GM^2}{2R^2} at 45∘45^\circ to the radius, plus F2=GM24R2F_2 = \frac{GM^2}{4R^2} along it.
  3. Net: F=2F1cos⁡45∘+F2=GM24R2(22+1)F = 2F_1\cos 45^\circ + F_2 = \frac{GM^2}{4R^2}(2\sqrt{2}+1).
  4. Mv2R=F⇒v=12GMR(22+1)\frac{Mv^2}{R} = F \Rightarrow v = \frac{1}{2}\sqrt{\frac{GM}{R}(2\sqrt{2}+1)}.
  5. So the answer is (b).
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