Gravitation is a core and high-weightage chapter in Class 11 Physics that explains the universal force of attraction between masses. This chapter covers key topics such as Newton’s law of gravitation, acceleration due to gravity, variation of g, gravitational potential and potential energy, escape velocity, orbital velocity, and Kepler’s laws of planetary motion—all crucial for school exams and competitive exams like JEE and NEET.
NCERT Solutions for Class 11 Physics Chapter 7 – Gravitation are prepared strictly according to the latest CBSE syllabus and exam pattern. The solutions are written in simple, step-by-step language with clear derivations, diagrams, and solved numericals, helping students build strong conceptual clarity and problem-solving skills.
NCERT Solutions for Class 11 Physics Chapter 7 – Gravitation
Q.
Answer the following:
(a) You can shield a charge from electrical forces by putting it inside a hollow conductor. Can you shield a body from the gravitational influence of nearby matter by putting it inside a hollow sphere or by some other means?
(b) An astronaut inside a small space ship orbiting around the earth cannot detect gravity. If the space station orbiting around the earth has a large size, can he hope to detect gravity?
(c) If you compare the gravitational force on the earth due to the sun to that due to the moon, you would find that the Sun’s pull is greater than the moon’s pull. (You can check this yourself using the data available in the succeeding exercises).
However, the tidal effect of the moon’s pull is greater than the tidal effect of sun. Why?
Q.
A rocket is fired from the earth towards the sun. At what distance from the earth’s centre is the gravitational force on the rocket zero? Mass of the sun = 2 ×1030 kg, mass of the earth = 6 × 1024 kg. Neglect the effect of other planets etc. (orbital radius = 1.5 × 1011 m).
Q.
A spaceship is stationed on Mars. How much energy must be expended on the spaceship to launch it out of the solar system? Mass of the space ship = 1000 kg; mass of the Sun = 2 × 1030 kg; mass of mars = 6.4 × 1023 kg; radius of mars = 3395 km; radius of the orbit of mars = 2.28 × 108 kg; G = 6.67 × 10–11 Nm2kg–2.
Q.
The escape speed of a projectile on the earth’s surface is 11.2 kms–1. A body is projected out with thrice this speed. What is the speed of the body far away from the earth? Ignore the presence of the sun and other planets.
Q.
A rocket is fired vertically with a speed of 5 kms–1 from the earth’s surface. How far from the earth does the rocket go before returning to the earth? Mass of the earth = 6.0 × 1024 kg; mean radius of the earth = 6.4 × 106 m; G= 6.67 × 10–11 Nm2kg–2.
Q.
Assuming the earth to be a sphere of uniform mass density, how much would a body weigh half way down to the centre of the earth if it weighed 250 N on the surface?
Q.
A body weighs 63 N on the surface of the earth. What is the gravitational force on it due to the earth at a height equal to half the radius of the earth?
Q.
A saturn year is 29.5 times the earth year. How far is the saturn from the sun if the earth is 1.50×108 km away from the sun?
Q.
How will you ‘weigh the sun’, that is estimate its mass? The mean orbital radius of the earth around the sun is 1.5 × 108 km.
Q.
Choose the correct answer from among the given ones:
For the problem 8.10, the direction of the gravitational intensity at an arbitrary point P is indicated by the arrow (i) d, (ii) e, (iii) f, (iv) g.
Q.
Choose the correct alternative:
(a) Acceleration due to gravity increases/decreases with increasing altitude.
(b) Acceleration due to gravity increases/decreases with increasing depth. (assume the earth to be a sphere of uniform density).
(c) Acceleration due to gravity is independent of the mass of the earth/mass of the body.
(d) The formula –GMm(1/r2 – 1/r1) is more/less accurate than the formula mg(r2 – r1) for the difference of potential energy between two points r2 and r1 distance away from the centre of the earth.
Q.
In the following two exercises, choose the correct answer from among the given ones:
The gravitational intensity at the centre of a hemispherical shell of uniform mass density has the direction indicated by the arrow (see Fig 8.12) (i) a, (ii) b, (iii) c, (iv) 0.
Q.
Which of the following symptoms is likely to afflict an astronaut in space (a) swollen feet (b) swollen face, (c) headache, (d) orientational problem?
Q.
A comet orbits the Sun in a highly elliptical orbit. Does the comet have a constant (a) linear speed, (b) angular speed, (c) angular momentum, (d) kinetic energy, (e) potential energy, (f) total energy throughout its orbit? Neglect any mass loss of the comet when it comes very close to the Sun.
Q.
Does the escape speed of a body from the earth depend on (a) the mass of the body, (b)the location from where it is projected, (c) the direction of projection, (d) the height of the location from where the body is launched?
Q.
Choose the correct alternative:
(a) If the zero of potential energy is at infinity, the total energy of an orbiting satellite is negative of its kinetic/potential energy.
(b) The energy required to launch an orbiting satellite out of earth’s gravitational influence is more/less than the energy required to project a stationary object at the same height (as the satellite) out of earth’s influence.
Q.
Let us assume that our galaxy consists of 2.5 × 1011 stars each of one solar mass. How long will a star at a distance of 50,000 ly from the galactic centre take to complete one revolution? Take the diameter of the Milky Way to be 105 ly.
Q.
Io, one of the satellites of Jupiter, has an orbital period of 1.769 days and the radius of the orbit is 4.22 × 108 m. Show that the mass of Jupiter is about one-thousandth that of the sun.
Q.
Suppose there existed a planet that went around the sun twice as fast as the earth. What would be its orbital size as compared to that of the earth?
Q.
A rocket is fired ‘vertically’ from the surface of mars with a speed of 2 kms–1. If 20% of its initial energy is lost due to Martian atmospheric resistance, how far will the rocket go from the surface of mars before returning to it? Mass of mars = 6.4×1023 kg; radius of mars = 3395 km; G = 6.67× 10-11 Nm2kg2.
Q. 1) Answer the following:
(a) You can shield a charge from electrical forces by putting it inside a hollow conductor.
Can you shield a body from the gravitational influence of nearby matter by putting it inside a hollow sphere or by some other means?
Ans: Gravitational influence of matter on nearby objects cannot be shielded by any means.
This is due to the fact that gravitational force is independent of the nature of the material medium, however, it is not so in the case of the electrical forces.
It is also independent of the presence of other objects.
(b) An astronaut inside a small space ship orbiting around the earth cannot detect gravity.
If the space station orbiting around the earth has a large size, can he hope to detect gravity?
Ans: Yes, if the size of the space ship orbiting around the Earth is very large, then the astronaut can identify the change in Earth’s gravity (g).
(c) If you compare the gravitational force on the earth due to the sun to that due to the moon, you would find that the Sun’s pull is greater than the moon’s pull.
However, the tidal effect of the moon’s pull is greater than the tidal effect of sun. Why?
Ans: Tidal effect is inversely proportional to the cube of the distance.
However, the gravitational force is inversely proportional to the square of the distance.
The distance between the Moon and the Earth is very small in comparison to the distance between the Sun and the Earth.
Therefore, the tidal effect of the Moon’s pull is more than the tidal effect of the Sun’s pull.
Q. 2) Choose the correct alternative:
(a) If the zero of potential energy is at infinity, the total energy of an orbiting satellite is negative of its kinetic/potential energy.
Ans: The total mechanical energy of a satellite is equal to the sum of its kinetic energy (always positive) and potential energy (maybe negative).
The gravitational P.E. of the satellite is zero at infinity.
The total energy of the satellite is negative as the Earth-satellite system is a bound system.
Therefore, at infinity, the total energy of an orbiting satellite is equal to the negative of its kinetic energy.
(b) The energy required to launch an orbiting satellite out of earth’s gravitational influence is more/less than the energy required to project a stationary object at the same height (as the satellite) out of earth’s influence.
Ans: An orbiting satellite attains a definite amount of energy that enables it to revolve around the Earth.
This energy is provided by the orbit of the satellite.
It needs relatively lesser energy to move out of the effect of the Earth’s gravitational field than a stationary object on the Earth’s surface that initially contains no energy.
Q. 3) A comet orbits the Sun in a highly elliptical orbit. Does the comet have a constant
(a) linear speed, (b) angular speed, (c) angular momentum, (d) kinetic energy, (e) potential energy, (f) total energy throughout its orbit?
Neglect any mass loss of the comet when it comes very close to the Sun.
Ans: For the given situation, the comet has constant values of angular momentum and total energy at all points of the orbit.
But, its linear speed, angular speed, kinetic, and potential energy change with locations in the orbit.
Q. 4) Which of the following symptoms is likely to afflict an astronaut in space
(a) swollen feet (b) swollen face, (c) headache, (d) orientational problem?
Ans: The symptoms (b), (c), and (d) can afflict an astronaut in space.
(a) Legs carry the weight of the body in a standing position because of gravitational pull.
The astronaut in space is in weightlessness state because of the absence of gravity.
Thus, swollen feet do not affect an astronaut in space.
(b) A swollen face is caused because of apparent weightlessness in space.
Since the sense organs such as eyes, ears nose, and mouth constitute a person’s face, hence, the swollen face can affect to great extent the seeing, hearing, smelling and eating capabilities of an astronaut in space.
(c) Headache is caused due to mental strain.
The headache will have the same effect on the astronaut in space as on a person on earth, therefore, it can affect the working of an astronaut in space.
(d) Space has several orientations and frames of reference in space.
Hence, the orientation problems can seriously affect an astronaut in space.
Note: Q&A containing MathML or Latex or Katex code cannot be rendered in pdf document.
FAQs: Class 11 Physics Chapter 7 – Gravitation
Q1. Is Gravitation important for exams?
Yes, it is a high-weightage mechanics chapter for Class 11, JEE, and NEET.
Q2. Which topics are most important in this chapter?
Newton’s law, Kepler’s laws, escape velocity, and orbital motion.
Q3. Are numericals asked from this chapter?
Yes, g-variation, satellite motion, and energy-based numericals are common.
Q4. Are derivations important here?
Yes, derivations of g, escape velocity, and orbital velocity are frequently asked.
Q5. How do NCERT Solutions help?
They provide NCERT-aligned, exam-ready explanations with solved numericals and diagrams.