NCERT Solutions Class 11 Physics Chapter 7 Gravitation

The Class 11 Physics NCERT Solutions Chapter 7 Gravitation will help students prepare for Boards, JEE Main, JEE Advanced, NEET, CUET and NDA in 2026-27. Every back-exercise question is solved with full working, so students can check each force calculation, gravity variation, potential energy step, and escape-velocity numerical one line at a time.

This chapter links the fall of an apple to the orbit of the Moon, and its formulas return again in later mechanics and space-physics questions.

• CBSE Weightage: 6 to 8 marks, usually one derivation plus one numerical on gravity, orbits or escape velocity.
• Questions solved: all Exercise 7.1 onward, covering Newton's law, Kepler's laws, gravity variation, potential energy, and satellites.
• Key formulas: universal gravitation, g variation with height and depth, escape velocity, orbital velocity, geostationary orbit.

Each solution in this Class 11 Physics NCERT Solutions Chapter 7 Gravitation compilation is curated by subject experts, based on the 2026-27 NCERT textbook, and refined against the last five years of CBSE Board, JEE Main and NEET papers.

Newton's Universal Law of Gravitation and the Gravitational Constant

The chapter opens with a single rule that holds for every pair of masses in the universe. Newton's law of gravitation says two point masses attract each other along the line joining them. Getting this force expression right is the first step in almost every numerical in the chapter.

The force between two masses m₁ and m₂ a distance r apart is F = G m₁m₂ / r². The constant G is the same everywhere, which is why the law is called universal.

• Direction: the force is always attractive and acts along the line joining the two centres.
• Inverse-square: double the distance and the force drops to one quarter.
• Gravitational constant: G = 6.67 × 10^-11 N m² kg^-2, found by Cavendish.

Questions such as Exercise 7.1 ask students to compare the gravitational pull in different situations. Treat a uniform sphere as if its whole mass sits at its centre. The solved answers state this shell result before substituting numbers, so the distance in the formula is never measured from the wrong point.

Kepler's Three Laws of Planetary Motion

Before Newton, Kepler described how planets actually move using three laws drawn from observation. The NCERT solutions use these laws in every orbit and period question, so students must know all three by name and by meaning.

• Law of orbits: every planet moves in an ellipse with the Sun at one focus.
• Law of areas: the line from the Sun to a planet sweeps equal areas in equal times, so a planet moves faster when it is nearer the Sun.
• Law of periods: the square of the time period is proportional to the cube of the semi-major axis, T² ∝ r³.

The law of areas is really the conservation of angular momentum, since gravity is a central force with no torque about the Sun. Numericals like Exercise 7.2 use the third law to compare the periods or distances of two planets. The ratio method is the fastest route: write T²/r³ as a constant and cancel. The solutions show the cancellation in full so no step is skipped.

Acceleration Due to Gravity and Its Variation with Height, Depth and Latitude

The value of g at the Earth's surface comes straight from the law of gravitation: g = G M / R², where M and R are the mass and radius of the Earth. But g is not fixed. The chapter tests how it changes with position, and the NCERT answers cover every case.

A common trap is that gravity falls off in both directions from the surface, up into the sky and down into the Earth, but by different rules. At the centre of the Earth, g is zero. Questions such as Exercise 7.6 ask for the value of g at a given altitude, and the solutions pick the height or depth formula first, then substitute, so students never mix the two.

Gravitational Potential Energy and Gravitational Potential

Lifting a mass against gravity stores energy. Near the surface this is just mgh, but for large distances the chapter uses the full form. The NCERT solutions apply it to escape problems, binding energy, and satellite energy.

The gravitational potential energy of two masses a distance r apart is U = − G M m / r. The minus sign matters: it shows the two masses are bound, and that energy must be added to pull them apart.

• Potential energy: U = − G M m / r, taken as zero at infinite separation.
• Gravitational potential: the energy per unit mass, V = − G M / r.
• Work done: to move a mass between two points, use the change in potential energy, not the force.

The value at infinity is chosen as zero, so every bound position has a negative potential energy. A more negative energy means a more tightly bound system. The Class 11 Physics NCERT Solutions Chapter 7 Gravitation keep the sign on every line, because dropping the minus sign is the single most common error in energy numericals here.

Escape Velocity and Orbital Velocity of a Satellite

Two speeds dominate the numerical part of the chapter. Escape velocity is the least speed a body needs to leave a planet for good. Orbital velocity is the speed a satellite needs to stay in a circular orbit. Both come from energy and force balance, and the NCERT solutions derive each one before using it.

The two are linked by a clean result: v_e = √2 × v_o. For the Earth the escape speed is about 11.2 km/s, and it does not depend on the mass or the direction of launch of the escaping body. Numericals such as Exercise 7.10 ask students to find the escape speed for a given planet. The solutions show the √(2g R) form, which avoids needing the mass of the planet at all.

Earth Satellites, Geostationary Orbits and Weightlessness

The last part of the chapter puts a real satellite in orbit and studies its energy. These ideas appear in short-answer questions and in one-mark objective items for JEE Main and NEET. The NCERT solutions explain each with reasoning a student can reproduce.

• Time period: a satellite at height h has T = 2π √((R+h)³/G M).
• Geostationary satellite: orbits with a period of 24 hours over the equator, so it appears fixed in the sky, at a height near 36,000 km.
• Total energy: for a circular orbit E = − G M m / 2(R+h), negative because the satellite is bound.
• Weightlessness: an astronaut feels weightless because both the astronaut and the satellite fall towards Earth with the same acceleration.

Weightlessness is not the absence of gravity. Gravity is still strong in orbit; the astronaut simply has no support force pressing back. The solutions state this reason clearly so students do not write that "there is no gravity in space", a marked error in the board scheme.

Exercise-wise Breakdown for Class 11 Physics Chapter 7 Gravitation

The NCERT back-exercise splits into clear groups. Use this map to plan which answers to practise first for the 2026-27 boards. Every group links to the full solved set.

Solving the groups in this order builds the skills in the same sequence the chapter teaches them. Start with the law, then gravity variation, then energy and satellites, because each group uses the one before it.

Common Mistakes Students Make in the Gravitation Chapter

These slips happen while writing or calculating the answer, not because the concept is unclear. Each one costs 1 to 3 marks in the CBSE paper, so the solved answers point them out at the exact step.

Student Feedback on the Gravitation Chapter

Practice Questions for Class 11 Physics Chapter 7 Gravitation

Once the solved answers are clear, test yourself on the full question set. The practice page has every NCERT question with a step-by-step Solution and an Expert Solution behind a click.

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