NCERT Solutions for Class 11 Physics Ch-7: Gravitation

Answer: Newton's law of universal gravitation states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them: F = Gm1m2/r², where G is the universal gravitational constant.

Answer: Kepler's first law (Law of Orbits) states that planets move in elliptical orbits with the Sun at one focus. Kepler's second law (Law of Areas) states that the line joining a planet to the Sun sweeps out equal areas in equal time intervals. Kepler's third law (Law of Periods) states that the square of a planet's orbital period is proportional to the cube of the semi-major axis of its orbit.

Answer: Acceleration due to gravity decreases both with an increase in height above the Earth's surface (approximately as g' = g(1 − 2h/R) for small heights) and with an increase in depth below the surface (as g' = g(1 − d/R)), becoming zero at the Earth's centre.

Answer: Escape velocity is the minimum velocity required for an object to escape a planet's gravitational field without further propulsion. It is derived by equating kinetic energy to gravitational potential energy: (1/2)mve² = GMm/R, giving ve = √(2GM/R), where M and R are the mass and radius of the planet.

Answer: A geostationary satellite is an artificial satellite that orbits the Earth in the equatorial plane with the same angular velocity as the Earth's rotation, completing one orbit in 24 hours, so it appears stationary relative to a fixed point on the Earth's surface.