🔹 Very Short Answer (1 mark)
Q1. What is gravitation?
Ans. The attractive force by which every object in the universe pulls every other object towards itself.
Q2. Who formulated the law of gravitation?
Ans. Sir Isaac Newton.
Q3. What is the SI unit of gravitational force?
Ans. Newton (N).
Q4. Define acceleration due to gravity (g).
Ans. The acceleration produced in a body due to the gravitational pull of the Earth.
Q5. Value of g on Earth’s surface.
Ans. Approximately 9.8 m/s².
Q6. Name the factor on which weight of a body depends.
Ans. Mass of the body and acceleration due to gravity.
Q7. What is mass?
Ans. The amount of matter in a body, constant everywhere.
Q8. What is weight?
Ans. Force with which a body is pulled towards Earth, W = mg.
Q9. Why is weight a force?
Ans. Because it has magnitude and direction (towards Earth).
Q10. What is free fall?
Ans. Motion of a body under gravity alone, without resistance of air.
🔹 Short Answer (2–3 marks)
Q11. State the universal law of gravitation.
Ans. Every particle in the universe attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them:
F = G * (m₁m₂)/r²
Q12. Define gravitational constant (G).
Ans. G = 6.67 × 10⁻¹¹ N·m²/kg², proportionality constant in Newton’s law.
Q13. Difference between mass and weight.
| Mass | Weight |
|---|---|
| Amount of matter | Force due to gravity |
| Constant everywhere | Varies with g |
| Unit: kg | Unit: N |
Q14. What happens to weight if body goes to Moon?
Ans. Weight decreases because g on Moon is 1/6th of Earth.
Q15. What is the shape of Earth due to gravitation?
Ans. Nearly spherical, slightly flattened at poles due to rotation.
Q16. What is escape velocity?
Ans. Minimum velocity required to leave Earth’s gravitational field without further propulsion.
Q17. Why do objects fall towards Earth?
Ans. Because of the gravitational pull of Earth.
Q18. What is the difference between free fall and motion under gravity?
Ans.
- Free fall: only gravity acts, no air resistance.
- Motion under gravity: air resistance may act.
Q19. What is a satellite?
Ans. A body that revolves around another body due to gravitational attraction.
Q20. What is the difference between natural and artificial satellite?
Ans.
- Natural: Moon (orbits Earth).
- Artificial: Man-made, e.g., INSAT, GPS satellites.
🔹 Long Answer (4–5 marks)
Q21. Explain why objects fall with same acceleration in free fall.
Ans. Because gravitational acceleration is independent of mass; g acts equally on all bodies near Earth.
Q22. Derive relation between weight and mass.
Ans. W = mg, where W = weight, m = mass, g = acceleration due to gravity.
Q23. Differentiate mass and weight with example.
| Mass | Weight |
|---|---|
| Amount of matter | Force acting on body due to gravity |
| Constant | Varies with g |
| Eg: 10 kg | Eg: 98 N on Earth |
Q24. State Newton’s law of gravitation and explain.
Ans. F = G * (m₁m₂)/r². Force is directly proportional to masses, inversely to square of distance.
Q25. Why does Earth’s gravity decrease with height?
Ans. As distance from Earth’s center increases, r increases → F ∝ 1/r² → g decreases.
Q26. Explain weightlessness in space.
Ans. In orbit, both satellite and astronaut fall together → no reaction force → feels weightless.
Q27. Differentiate between gravitation and gravity.
| Gravitation | Gravity |
|---|---|
| Universal | Earth-specific |
| Follows inverse-square law | Acceleration g acts downward |
Q28. Define escape velocity of Earth.
Ans. Minimum velocity a body must have to overcome Earth’s gravity without further propulsion: v = √(2gR).
Q29. What is the value of g at surface of Moon?
Ans. 1.6 m/s² (~1/6th of Earth).
Q30. Explain why moon does not fall on Earth.
Ans. It has tangential velocity, creating circular orbit; gravitational pull provides centripetal force.
🔹 Case Study / Application-Based (5–6 marks)
Q31. Case Study – Weight on Moon
A person weighs 60 kg on Earth.
(i) Will weight be same on Moon?
(ii) Explain.
Ans.
(i) No, weight decreases.
(ii) Because Moon’s g = 1/6th Earth → W = mg decreases.
Q32. Why astronauts appear weightless in space?
Ans. They are in free fall along with spacecraft → no support force acts → weightlessness.
Q33. Case Study – Falling Apple
Apple falls from tree → Newton conceptualized gravity.
(i) Why apple falls?
(ii) Which law of motion explains it?
Ans.
(i) Earth’s gravitational pull.
(ii) Second law (F = ma).
Q34. Why does a satellite orbit around Earth instead of falling?
Ans. Tangential velocity → centripetal acceleration due to gravity → circular motion.
Q35. Why is g slightly less at poles compared to equator?
Ans. Earth’s rotation → centrifugal force reduces effective gravity at equator.
Q36. Why does gravitational force exist between any two objects?
Ans. Because all matter has mass → attracts each other.
Q37. Why does weight vary with height above Earth?
Ans. g ∝ 1/r², as r increases with height, weight decreases.
Q38. Why is acceleration due to gravity constant near Earth’s surface?
Ans. Because height << Earth’s radius → negligible variation in g.
Q39. How does mass affect gravitational force?
Ans. Greater mass → greater gravitational attraction.
Q40. Why are Earth and Moon spherical in shape?
Ans. Gravity pulls matter equally from all directions → forms sphere.
🔹 Extra Important (41–50)
Q41. Define universal gravitation.
Ans. Force of attraction between any two particles in the universe.
Q42. Give formula for gravitational force.
Ans. F = G * (m₁m₂)/r²
Q43. Name two natural satellites of Earth and Jupiter.
Ans. Earth: Moon. Jupiter: Io, Europa (any two).
Q44. What happens to weight of a body at Earth’s center?
Ans. Weight = 0, because net gravitational pull from all sides cancels out.
Q45. Define centripetal force in context of satellite motion.
Ans. Gravity acts as centripetal force keeping satellite in orbit.
Q46. Why does a body in free fall accelerate downwards?
Ans. Only force acting is gravity → acceleration = g.
Q47. Why do objects of different masses fall with same acceleration in vacuum?
Ans. Gravity acts equally on all → no air resistance.
Q48. What is the difference between artificial and natural satellite?
Ans. Natural: Moon. Artificial: Man-made, used for communication, GPS.
Q49. How does distance between objects affect gravitational force?
Ans. F ∝ 1/r² → greater distance, smaller force.
Q50. Why is gravity important for life on Earth?
Ans. Keeps atmosphere, oceans, objects on Earth; allows satellite motion; governs planetary motion.