UPSC NDA I 2023 General Ability Solved Paper

Concept:Newton’s third law and the universal law of gravitation explain that the gravitational force between two bodies is equal in magnitude but opposite in direction.Explanation:According to the universal law of gravitation, the force between the Earth and the Moon is given by $F = G \frac{M_{\text{Earth}} M_{\text{Moon}}}{r^2}$.This force acts on both bodies equally in magnitude.Newton’s third law states that every action has an equal and opposite reaction.Therefore, the force of gravity of the Earth on the Moon and the force of gravity of the Moon on the Earth are equal in magnitude ($F_{\text{Earth on Moon}} = F_{\text{Moon on Earth}}$).However, they act in opposite directions — the Earth pulls the Moon toward it, and the Moon pulls the Earth toward it.Hence, the forces are not in the same direction; they are opposite.Options A and B incorrectly claim one force is greater than the other.Option C incorrectly states the forces are in the same direction.Option D correctly states that the forces are equal in magnitude but opposite in direction.Answer:Option D — The force of gravity of the Earth on the Moon and of the Moon on the Earth are equal in magnitude but are in opposite directions.