The masses of two planets are in the ratio of 1 : 7. The ratio between

The masses of two planets are in the ratio of 1 : 7. The ratio between their diameters is 2 : 1. The ratio of forces which they exert on each other is

1 : 7
7 : 1
1 : 1
2 : 1
This question was previously asked in
UPSC NDA-2 – 2024
The correct answer is C) 1 : 1.
According to Newton’s Third Law of Motion and Newton’s Law of Universal Gravitation, the force exerted by the first planet on the second planet is equal in magnitude to the force exerted by the second planet on the first planet. This holds true regardless of the masses or distances of the objects involved in the gravitational interaction.
The force of gravity between two objects with masses m₁ and m₂ separated by a distance r is given by the formula F = G * (m₁ * m₂) / r². The force exerted by planet 1 on planet 2 (F₁₂) is equal to G * (m₁ * m₂) / r², and the force exerted by planet 2 on planet 1 (F₂₁) is also equal to G * (m₂ * m₁) / r². Therefore, F₁₂ = F₂₁, and the ratio of the forces they exert on each other is always 1:1. The information about the ratio of masses and diameters is extraneous to the question about the ratio of forces *between* them.