UPSC NDA I 2019 General Ability Solved Paper

Concept:A black hole is a collapsed star with extreme gravity.Gravity on its surface gives a very large acceleration due to gravity.Explanation:The acceleration due to gravity $g$ on a star’s surface is $g = \frac{GM}{R^2}$, where $M$ is mass and $R$ is radius.When a massive star collapses, its radius becomes extremely small while its mass remains large.This makes $g$ enormous—often approaching infinity.A black hole’s gravity is so strong that it pulls in everything, including light.Thus, the black hole has a very large acceleration due to gravity on its surface.Answer:Option C: star which has collapsed into itself and has large acceleration due to gravity on its surface.