UPSC NDA 2 2017 General Ability Solved Paper

Concept:A satellite in orbit is balanced between Earth's gravitational pull and its own centrifugal force, so it requires no external energy to maintain its motion.Explanation:The satellite moves in a circular path around Earth.Earth's gravity provides the centripetal force needed for this circular motion.The satellite's orbital speed generates a centrifugal force that exactly opposes gravity.These two forces are equal and opposite: $F_{\text{gravity}} = \frac{G M m}{r^{2}}$ and $F_{\text{centrifugal}} = \frac{m v^{2}}{r}$.In a stable orbit, $\frac{G M m}{r^{2}} = \frac{m v^{2}}{r}$, meaning no external work is done to keep it moving.Thus, the satellite orbits due to inertia and gravitational balance, without needing any energy.Other options are incorrect: remote control, retro-rockets, or solar panels are used for adjustments or power, not for the orbital motion itself.Answer:Option D: Satellite does not require any energy for orbiting.