Gravitation is the force of attraction between any two masses. Important Questions Class 11 Physics Chapter 7 help students understand why objects fall towards Earth, why planets move around the Sun and why satellites remain in orbit.
Important Questions Class 11 Physics Chapter 7 help students practise Gravitation through definitions, laws, formulas, numericals and reasoning questions.
This chapter connects falling bodies on Earth with planetary motion in space. Galileo studied falling bodies, Kepler described planetary orbits, and Newton explained both through the universal law of gravitation.
Students should revise this chapter with formula clarity because many questions involve g, orbital speed, escape speed, satellite energy and variation of gravity. These questions help students prepare for 2026 exams with concept-based answers and numerical practice.
Key Takeaways from Important Questions Class 11 Physics Chapter 7
| Area |
What Students Should Revise |
| Chapter Name |
Gravitation |
| Chapter Number |
Chapter 7 |
| Main Idea |
Attractive force between masses |
| Important Laws |
Kepler’s laws and universal law of gravitation |
| Important Constant |
G = 6.67 × 10⁻¹¹ N m² kg⁻² |
| Scoring Topics |
Variation of g, escape speed, satellites and energy |
| Main Numericals |
Force, g, potential energy, escape speed, orbital speed |
| Common Mistake |
Confusing G with g |
| Best Practice |
Learn formulas with meaning, units and conditions |
Gravitation Formulas Class 11
Students should revise gravitation formulas class 11 before solving numericals. Many formulas look similar, so students should check whether the question asks force, g, energy, escape speed or orbital speed.
| Concept |
Formula |
| Universal law of gravitation |
F = Gm₁m₂/r² |
| Value of G |
6.67 × 10⁻¹¹ N m² kg⁻² |
| Acceleration due to gravity |
g = GMₑ/Rₑ² |
| g at height h |
g(h) = GMₑ/(Rₑ + h)² |
| g at small height h |
g(h) ≈ g(1 − 2h/Rₑ) |
| g at depth d |
g(d) = g(1 − d/Rₑ) |
| Gravitational potential energy |
U = −GMm/r |
| Near Earth potential energy |
U = mgh |
| Escape speed |
ve = √(2GMₑ/Rₑ) = √(2gRₑ) |
| Orbital speed |
v = √[GMₑ/(Rₑ + h)] |
| Time period of satellite |
T = 2π(Rₑ + h)³ᐟ²/√GMₑ |
| Satellite kinetic energy |
K = GMₑm/2r |
| Satellite potential energy |
U = −GMₑm/r |
| Total energy of satellite |
E = −GMₑm/2r |
Important Questions CBSE Class 11 Physics Chapter-Wise
Gravitation Class 11 Important Questions on Kepler’s Laws
Gravitation class 11 important questions often start with Kepler’s laws. These laws describe planetary motion and prepare students for Newton’s law of gravitation.
Q1. State Kepler’s first law of planetary motion.
Kepler’s first law states that every planet moves in an elliptical orbit with the Sun at one focus.
Q2. What is Kepler’s second law?
Kepler’s second law states that the line joining a planet and the Sun sweeps equal areas in equal intervals of time.
Q3. What is Kepler’s third law?
Kepler’s third law states that the square of the time period of a planet is proportional to the cube of the semi-major axis of its orbit.
T² ∝ a³
Q4. What does Kepler’s second law show about planetary speed?
A planet moves faster near the Sun and slower when it is farther away. This follows from equal areas in equal intervals of time.
Q5. Which conservation law explains Kepler’s second law?
Conservation of angular momentum explains Kepler’s second law. Gravitational force acts as a central force.
Q6. What is the difference between perihelion and aphelion?
Perihelion is the closest point of a planet from the Sun. Aphelion is the farthest point.
Q7. Why is a circular orbit a special case of an elliptical orbit?
A circle is an ellipse with both foci at the same point. So, a circular orbit is a special elliptical orbit.
Kepler Laws Class 11 Questions with Answers
Kepler laws class 11 questions also test the relation between time period and orbital radius. Students should know how to apply T² ∝ R³ in direct numericals.
Q8. If a planet’s orbital radius becomes four times, how does its time period change?
Using Kepler’s third law:
T² ∝ R³
If R becomes 4R, then:
T² becomes 4³ = 64 times
T becomes 8 times.
Answer: The time period becomes 8 times.
Q9. Why does a planet not move with constant linear speed in an elliptical orbit?
The planet’s distance from the Sun changes in an elliptical orbit. It moves faster near the Sun and slower away from it.
Q10. Is angular momentum conserved in planetary motion?
Yes. Angular momentum is conserved because gravitational force acts along the line joining the Sun and the planet.
Q11. Does Kepler’s third law apply to satellites?
Yes. Kepler’s third law applies to satellites around Earth. The central mass changes from the Sun to Earth.
Q12. What is the physical meaning of equal areas in equal times?
It means the planet covers different arc lengths in the same time. It moves faster when it is closer to the Sun.
Universal Law of Gravitation Class 11 Questions
Universal law of gravitation class 11 questions are central to this chapter. Students should know the statement, formula, vector nature and units.
Q13. State Newton’s universal law of gravitation.
Every body in the universe attracts every other body with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Q14. Write the formula for gravitational force.
The formula is:
F = Gm₁m₂/r²
Here, G is the universal gravitational constant.
Q15. Why is gravitational force called universal?
It acts between every pair of masses in the universe. It applies to objects on Earth, planets, stars and satellites.
Q16. Is gravitational force attractive or repulsive?
Gravitational force is always attractive. It pulls masses towards each other.
Q17. What happens to gravitational force if distance doubles?
Force becomes one-fourth.
F ∝ 1/r²
So, when r becomes 2r, force becomes F/4.
Q18. What happens to gravitational force if both masses double?
Force becomes four times because force is proportional to the product of masses.
Q19. Why do two students sitting in a classroom not feel gravitational attraction between them?
The attraction exists, but it is extremely small. Human masses are small compared with Earth’s mass.
Gravitational Constant Class 11 Questions
Gravitational constant class 11 questions usually test value, unit, dimensional formula and Cavendish experiment.
Q20. What is the value of universal gravitational constant?
G = 6.67 × 10⁻¹¹ N m² kg⁻²
Q21. What is the SI unit of G?
The SI unit of G is N m² kg⁻².
Q22. Write the dimensional formula of G.
The dimensional formula of G is [M⁻¹L³T⁻²].
Q23. Who first measured the value of G?
Henry Cavendish first measured the value of G using a torsion balance experiment.
Q24. Why is G called a universal constant?
G has the same value for all masses and all places. It does not depend on the nature of the objects.
Q25. What is the difference between G and g?
G is the universal gravitational constant. g is acceleration due to gravity at a place.
G remains constant everywhere. g changes with height, depth and location.
Acceleration Due to Gravity Class 11 Questions
Acceleration due to gravity class 11 questions test the meaning of g and its relation with Earth’s mass and radius.
Q26. What is acceleration due to gravity?
Acceleration due to gravity is the acceleration produced in a body due to Earth’s gravitational attraction.
Q27. Write the formula for g at Earth’s surface.
g = GMₑ/Rₑ²
Here, Mₑ is Earth’s mass and Rₑ is Earth’s radius.
Q28. Why does g not depend on the mass of the falling body?
The gravitational force is proportional to the mass of the body. When F = mg is used, mass cancels out.
So, all bodies fall with the same acceleration if air resistance is neglected.
Q29. What is the approximate value of g near Earth’s surface?
The approximate value of g is 9.8 m s⁻².
Q30. Why did Galileo’s observation matter for gravitation?
Galileo showed that bodies fall with the same acceleration, independent of mass. This idea supports the concept of acceleration due to gravity.
Q31. Why is g maximum at Earth’s surface?
g decreases above Earth’s surface and also decreases below the surface. So, it has its maximum value at the surface.
Variation of g with Height and Depth Questions
Variation of g with height and depth questions are very important for Class 11 Physics exams. Students should not use the same formula for height and depth.
Q32. How does g change with height?
g decreases with height above Earth’s surface.
g(h) = GMₑ/(Rₑ + h)²
For small h:
g(h) ≈ g(1 − 2h/Rₑ)
Q33. How does g change with depth?
g decreases with depth below Earth’s surface.
g(d) = g(1 − d/Rₑ)
Q34. What is the value of g at Earth’s centre?
At Earth’s centre, d = Rₑ.
g(d) = g(1 − Rₑ/Rₑ) = 0
Answer: g is zero at Earth’s centre.
Q35. What is g at a depth equal to half Earth’s radius?
g(d) = g(1 − d/Rₑ)
d = Rₑ/2
g(d) = g(1 − 1/2) = g/2
Answer: g becomes half of its surface value.
Q36. Why does g decrease inside Earth?
Only the mass inside that depth contributes to gravitational attraction. The outer spherical shell exerts no net force.
Gravitation Class 11 Numericals on Force and g
Gravitation class 11 numericals often ask students to apply inverse-square law, g formula and height-depth variation.
Q37. Two masses 10 kg and 20 kg are separated by 2 m. Find gravitational force between them.
F = Gm₁m₂/r²
F = 6.67 × 10⁻¹¹ × 10 × 20 / 2²
F = 6.67 × 10⁻¹¹ × 200 / 4
F = 3.335 × 10⁻⁹ N
Answer: The force is 3.335 × 10⁻⁹ N.
Q38. If distance between two bodies becomes three times, what happens to force?
F ∝ 1/r²
If r becomes 3r, force becomes F/9.
Answer: Force becomes one-ninth.
Q39. A body weighs 100 N at Earth’s surface. What is its weight at depth Rₑ/4?
g(d) = g(1 − d/Rₑ)
d = Rₑ/4
g(d) = 3g/4
Weight = 100 × 3/4 = 75 N
Answer: Weight becomes 75 N.
Q40. If g at Earth’s surface is 9.8 m s⁻², find g at depth Rₑ/2.
g(d) = g(1 − d/Rₑ)
g(d) = 9.8(1 − 1/2)
g(d) = 4.9 m s⁻²
Answer: g becomes 4.9 m s⁻².
Gravitational Potential Energy Class 11 Questions
Gravitational potential energy class 11 questions test energy conservation and sign conventions.
Q41. What is gravitational potential energy?
Gravitational potential energy is energy stored due to the position of a mass in a gravitational field.
Q42. Write gravitational potential energy between two masses.
U = −Gm₁m₂/r
The value is negative when zero potential energy is taken at infinity.
Q43. Why is gravitational potential energy negative?
It is negative because gravity is attractive. Work must be done to separate masses to infinity.
Q44. What is the expression for gravitational potential energy near Earth’s surface?
For small heights near Earth:
U = mgh
This is an approximation.
Q45. Why is mgh only an approximation?
mgh assumes g remains constant. This works only when height is much smaller than Earth’s radius.
Q46. What is gravitational potential?
Gravitational potential at a point is gravitational potential energy per unit mass placed at that point.
Q47. What is total mechanical energy in a gravitational field?
Total mechanical energy is the sum of kinetic energy and gravitational potential energy.
E = K + U
Escape Velocity Class 11 Questions
Escape velocity class 11 questions are high-scoring because they use conservation of energy.
Q48. What is escape velocity?
Escape velocity is the minimum speed needed to project a body so it escapes Earth’s gravitational field.
Q49. Write the formula for escape speed from Earth.
ve = √(2GMₑ/Rₑ)
It can also be written as:
ve = √(2gRₑ)
Q50. What is the escape speed from Earth’s surface?
The escape speed from Earth’s surface is about 11.2 km s⁻¹.
Q51. Does escape speed depend on the mass of the body?
No. Escape speed does not depend on the mass of the body.
Q52. Does escape speed depend on direction of projection?
No. Escape speed depends on the initial location, not on the direction of projection.
Q53. Why does the Moon have no thick atmosphere?
The Moon has lower escape speed than Earth. Gas molecules can escape more easily from the Moon.
Gravitation Class 11 Questions and Answers on Earth Satellites
Gravitation class 11 questions and answers from satellites test circular motion and gravitational force together.
Q54. What is an earth satellite?
An earth satellite is an object that revolves around Earth in an orbit.
Q55. Name one natural satellite of Earth.
The Moon is Earth’s natural satellite.
Q56. What provides centripetal force to a satellite?
Earth’s gravitational force provides the centripetal force for satellite motion.
Q57. Why does a satellite not fall straight to Earth?
A satellite has enough tangential speed. It keeps falling towards Earth while moving forward, so it stays in orbit.
Q58. Write the formula for orbital speed of a satellite.
v = √[GMₑ/(Rₑ + h)]
Here, h is the height above Earth’s surface.
Q59. What happens to orbital speed as satellite height increases?
Orbital speed decreases as height increases.
Q60. What is the time period of a near-Earth satellite?
A near-Earth satellite has a time period of about 85 minutes.
Orbital Velocity Class 11 Questions
Orbital velocity class 11 questions often compare orbital speed with escape speed.
Q61. What is orbital velocity?
Orbital velocity is the speed needed by a satellite to move in a stable orbit around Earth.
Q62. Write orbital velocity close to Earth’s surface.
For h ≈ 0:
v = √(gRₑ)
Q63. How is escape speed related to orbital speed near Earth?
ve = √2 v₀
Here, v₀ is orbital speed close to Earth’s surface.
Q64. Is orbital velocity independent of satellite mass?
Yes. Orbital velocity does not depend on satellite mass.
Q65. Why does a higher satellite move slower?
A higher satellite is farther from Earth’s centre. Gravitational pull is weaker, so required orbital speed is lower.
Energy of Satellite Class 11 Questions
Energy of satellite class 11 questions test kinetic energy, potential energy and total energy in orbit.
Q66. Write kinetic energy of an orbiting satellite.
K = GMₑm/2r
Here, r = Rₑ + h.
Q67. Write potential energy of an orbiting satellite.
U = −GMₑm/r
Q68. Write total energy of an orbiting satellite.
E = −GMₑm/2r
Q69. Why is total energy of an orbiting satellite negative?
It is negative because the satellite remains bound to Earth. A bound system has negative total energy.
Q70. What is the relation between kinetic energy and potential energy of a satellite?
For a circular orbit:
K = −U/2
So, total energy is:
E = U/2 = −K
Q71. What happens to satellite energy when orbital radius increases?
Total energy becomes less negative. Energy must be supplied to move a satellite to a higher orbit.
Class 11 Gravitation Important Questions: Solved Numericals
These class 11 gravitation important questions mix force, escape speed, satellite speed and energy.
Important Questions Class 11 Physics Chapter 7: Numerical Practice
Practise these questions after revising force, g, escape speed, orbital speed and satellite energy formulas.
Q72. Find escape speed from a planet where g = 5 m s⁻² and R = 4 × 10⁶ m.
ve = √(2gR)
ve = √(2 × 5 × 4 × 10⁶)
ve = √(4 × 10⁷)
ve ≈ 6.32 × 10³ m s⁻¹
Answer: Escape speed is about 6.32 km s⁻¹.
Q73. Find orbital speed near Earth if g = 9.8 m s⁻² and Rₑ = 6.4 × 10⁶ m.
v = √(gRₑ)
v = √(9.8 × 6.4 × 10⁶)
v ≈ 7.9 × 10³ m s⁻¹
Answer: Orbital speed is about 7.9 km s⁻¹.
Q74. A satellite of mass 100 kg orbits Earth at radius r. Write its total energy.
E = −GMₑm/2r
E = −GMₑ(100)/2r
E = −50GMₑ/r
Answer: Total energy is −50GMₑ/r.
Q75. A body weighs 98 N on Earth. Find its mass. Take g = 9.8 m s⁻².
Weight = mg
98 = m × 9.8
m = 10 kg
Answer: The mass is 10 kg.
Q76. If Earth’s radius becomes half but mass remains same, what happens to g?
g = GM/R²
If R becomes R/2:
g′ = GM/(R/2)² = 4GM/R²
g′ = 4g
Answer: g becomes four times.
Gravitation Class 11 Extra Questions
These gravitation class 11 extra questions help students revise reasoning-based answers.
Q77. Why is gravitational force called a central force?
It acts along the line joining the centres of two masses.
Q78. Why does a body feel weightless in an orbiting satellite?
The body and satellite both fall freely towards Earth. This creates apparent weightlessness.
Q79. Can gravitational force be shielded?
No. Gravitational shielding is not possible.
Q80. Why is linear momentum not conserved for a satellite-Earth system if only the satellite is considered?
Earth exerts an external gravitational force on the satellite. So, satellite momentum alone does not remain conserved.
Q81. Why does a satellite need horizontal speed?
Horizontal speed prevents it from falling straight down. It keeps the satellite in orbit.
Q82. Why does gravitational force dominate planetary motion?
Gravity acts over very large distances and always attracts. This makes it dominant for planets and stars.
Q83. Why does a heavier body not fall faster than a lighter body in vacuum?
Both experience the same acceleration due to gravity. Mass cancels in the acceleration equation.
Class 11 Physics Gravitation Important Questions: Common Mistakes
Students often confuse G and g. G is universal and constant, while g changes with location.
Common mistakes include:
- Confusing universal gravitational constant with acceleration due to gravity
- Writing escape velocity when only escape speed is required
- Using mgh for large heights
- Forgetting that gravitational potential energy is negative
- Saying a satellite has zero gravity
- Using surface value of g at high altitudes
- Confusing orbital speed with escape speed
- Forgetting units in gravitation numericals
Do not say a satellite has zero gravity. Earth’s gravitational force provides the centripetal force needed for satellite motion.
Do not use mgh for distances comparable to Earth’s radius. Use U = −GMm/r instead.
Quick Revision Notes for Gravitation Questions Class 11
Gravitation is an attractive force between masses.
Kepler’s first law gives elliptical orbits.
Kepler’s second law shows conservation of angular momentum.
Kepler’s third law gives T² ∝ a³.
Newton’s law of gravitation gives F = Gm₁m₂/r².
Acceleration due to gravity is g = GMₑ/Rₑ².
g decreases with height and depth.
Gravitational potential energy is negative when zero is at infinity.
Escape speed from Earth is about 11.2 km s⁻¹.
Earth’s gravity provides centripetal force for satellites.
Total energy of an orbiting satellite is negative.