Introduction
Gravitation is an important chapter of Class 9 Physics that explains the force of attraction between masses. It covers Newton’s Law of Universal Gravitation, the gravitational constant, acceleration due to gravity, mass and weight, free fall, satellites, escape velocity, and planetary motion. Students also learn how gravity governs the motion of planets, keeps satellites in orbit, and influences many everyday phenomena.
These Class 9 Physics Chapter 5 MCQs are prepared according to the Punjab and Sindh Board syllabus to help students revise important concepts, strengthen problem-solving skills, and prepare confidently for board examinations.
Learning Outcomes
After studying this chapter, students will be able to:
- Explain Newton’s Law of Universal Gravitation.
- Define the gravitational constant (G).
- Differentiate between mass and weight.
- Explain acceleration due to gravity (g).
- Describe free fall and its characteristics.
- Understand the factors affecting gravitational acceleration.
- Explain the motion of satellites and planets.
- Describe escape velocity and its applications.
Quick Notes – Chapter Summary
- Gravitation is the force of attraction between any two masses.
- Newton’s Law of Universal Gravitation states that gravitational force is directly proportional to the product of masses and inversely proportional to the square of the distance between them.
- The universal gravitational constant (G) is 6.67 × 10⁻¹¹ N·m²/kg².
- Acceleration due to gravity on Earth is approximately 9.8 m/s².
- Weight depends on gravity, while mass remains constant everywhere.
- Free fall occurs when gravity is the only force acting on an object.
- Satellites remain in orbit due to Earth’s gravitational attraction.
- Escape velocity from Earth is approximately 11.2 km/s.
- Kepler’s laws describe the motion of planets around the Sun.
- Gravity influences tides, planetary motion, and artificial satellite operation.
Important Definitions
Gravitation: The force of attraction between any two masses.
Universal Gravitational Constant (G): The proportionality constant used in Newton’s Law of Universal Gravitation.
Acceleration Due to Gravity (g): The acceleration experienced by an object due to Earth’s gravitational pull.
Mass: The amount of matter present in a body.
Weight: The gravitational force acting on a body (W = mg).
Free Fall: Motion of a body under the influence of gravity alone.
Escape Velocity: The minimum velocity required for an object to escape Earth’s gravitational field without further propulsion.
Important Concepts
Kepler’s laws of planetary motion
Newton’s Law of Universal Gravitation
Universal gravitational constant (G)
Acceleration due to gravity (g)
Mass and weight
Free fall
Satellite motion
Escape velocity
Class 9 Physics Chapter 5 – Gravitation MCQs
1. Who proposed the law of universal gravitation?
- A. Isaac Newton ✅
- B. Albert Einstein
- C. Galileo Galilei
- D. Johannes Kepler
Explanation: Newton formulated the law of universal gravitation in the 17th century.
2. The law of gravitation states that the force between two bodies is:
- A. Directly proportional to the product of their masses ✅
- B. Directly proportional to the sum of their masses
- C. Inversely proportional to the square of their masses
- D. Independent of distance
Explanation: F ∝ m₁m₂ and inversely proportional to the square of the distance between them.
3. The SI unit of the gravitational constant (G) is:
- A. N·m²/kg² ✅
- B. N·m/kg
- C. m/s²
- D. N/kg
Explanation: G is measured in newton meter² per kilogram².
4. The value of G is:
- A. 6.67 × 10⁻¹¹ N·m²/kg² ✅
- B. 9.8 m/s²
- C. 3 × 10⁸ m/s
- D. 1.6 × 10⁻¹⁹ C
Explanation: G has a constant value of 6.67 × 10⁻¹¹ N·m²/kg².
5. Acceleration due to gravity on Earth is approximately:
- A. 9.8 m/s² ✅
- B. 10 m/s²
- C. 6.67 m/s²
- D. 8.9 m/s²
Explanation: The average value of g on Earth’s surface is 9.8 m/s².
6. Which factor does NOT affect the value of g?
- A. Mass of the object ✅
- B. Altitude
- C. Latitude
- D. Depth below the surface
Explanation: g is independent of the object’s mass.
7. Free fall occurs when:
- A. Only gravity acts on the body ✅
- B. Gravity and air resistance act together
- C. No force acts
- D. The body moves at constant velocity
Explanation: In free fall, only gravitational force influences motion.
8. Weight is defined as:
- A. Mass × acceleration due to gravity ✅
- B. Mass × velocity
- C. Mass × distance
- D. Force × area
Explanation: W = mg, measured in newtons.
9. The weight of a body on the Moon is about:
- A. One-sixth of its weight on Earth ✅
- B. Half of its weight on Earth
- C. Twice its weight on Earth
- D. The same as on Earth
Explanation: Moon’s gravity is about 1/6th of Earth’s.
10. Which quantity remains constant everywhere?
- A. Mass ✅
- B. Weight
- C. g
- D. Force
Explanation: Mass does not change with location.
11. The path of a satellite around Earth is:
- A. Elliptical ✅
- B. Circular only
- C. Straight
- D. Irregular
Explanation: Satellites follow elliptical orbits due to gravitational forces.
12. Who measured the value of G experimentally?
- A. Henry Cavendish ✅
- B. Galileo Galilei
- C. Kepler
- D. Newton
Explanation: Cavendish measured G using a torsion balance in 1798.
13. The escape velocity from Earth is about:
- A. 11.2 km/s ✅
- B. 9.8 km/s
- C. 7.9 km/s
- D. 15 km/s
Explanation: Escape velocity is the speed needed to leave Earth’s gravitational field without further propulsion.
14. Which of the following is a field force?
- A. Gravitational force ✅
- B. Frictional force
- C. Tension
- D. Normal force
Explanation: Gravitational force acts without physical contact between bodies.
15. Kepler’s laws are related to:
- A. Planetary motion ✅
- B. Falling bodies
- C. Tides
- D. Weight
Explanation: Kepler’s laws describe the motion of planets under gravitational attraction.
Exam Tips
- Memorize Newton’s Law of Universal Gravitation and its formula.
- Learn the difference between mass and weight.
- Remember the values of G (6.67 × 10⁻¹¹ N·m²/kg²) and g (9.8 m/s²).
- Understand the concepts of free fall, escape velocity, and satellite motion.
- Practice numerical problems involving gravitational force and weight.
Common Mistakes
❌ Confusing mass with weight.
❌ Mixing up the gravitational constant (G) with acceleration due to gravity (g).
❌ Thinking gravity disappears completely in space.
❌ Forgetting that weight changes with gravity while mass remains constant.
❌ Assuming satellites stay in orbit because there is no gravity.
Conclusion
Gravitation explains one of the four fundamental forces of nature and governs the motion of planets, moons, satellites, and all objects on Earth. Understanding Newton’s Law of Universal Gravitation, acceleration due to gravity, free fall, and orbital motion provides a strong foundation for higher-level physics. Regular practice of these MCQs will improve conceptual understanding and help students perform confidently in board examinations.