Q. Three identical bodies of mass $M$ are located at the vertices of an equilateral triangle of side $L$. They revolve under the effect of mutual gravitational force in a circular orbit, circumscribing the triangle while preserving the equilateral triangle. Their orbital velocity is

A) $\ \sqrt{\frac{GM}{L}}$
B) $\sqrt{\frac{3GM}{2L}}$
C) $\sqrt{\frac{3GM}{L}}$
D) $\sqrt{\frac{2GM}{3L}}$
Explanation

(a) Given, $F_{1} = F_{2} = F\ and\ \theta = 60{^\circ}$
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$Resultant\ force = \sqrt{3}\ F$
$\therefore Force\ on\ mass\ at\ A\ due\ to\ mass\ at\ B\ and\ C$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \sqrt{3}\left( \frac{{GM}^{2}}{L^{2}} \right)$
Centripetal force for circumscribing the triangle in a circular orbit is provided by mutual gravitational interaction.
$ie,\ \ \frac{{Mv}^{2}}{\left( L/\sqrt{3} \right)} = \sqrt{3}\left( \frac{{GM}^{2}}{L^{2}} \right)$
$or\ \ v = \sqrt{\frac{GM}{L}}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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