Gravitation Class 9 Science 20 Important Questions with answer

20 important questions with answers on the topic of Gravitation from the Class 9 Science curriculum:

1. What is the universal law of gravitation?

   • Answer: The universal law of gravitation states that every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Mathematically, it is expressed as $F = G \frac{m_1 m_2}{r^2}$, where $F$ is the gravitational force, $G$ is the gravitational constant, $m_1$ and $m_2$ are the masses of the two objects, and $r$ is the distance between their centers.

2. What is the value of the gravitational constant (G)?

   • Answer: The value of the gravitational constant $G$ is approximately $6.674 \times 10^{-11} \, \text{N m}^2 \text{kg}^{-2}$.

3. How does the gravitational force between two objects change if the distance between them is doubled?

   • Answer: According to the universal law of gravitation, if the distance between two objects is doubled, the gravitational force between them becomes one-fourth of the original force. This is because the force is inversely proportional to the square of the distance.

4. Why do objects fall towards the Earth?

   • Answer: Objects fall towards the Earth due to the gravitational force exerted by the Earth. This force pulls objects towards the Earth's center.

5. Explain how weight and mass are different.

   • Answer: Mass is the amount of matter in an object and is constant regardless of location. Weight is the force exerted by gravity on an object’s mass. Weight varies with the strength of the gravitational field, so it changes with location. The formula is $W = mg$, where $W$ is weight, $m$ is mass, and $g$ is the acceleration due to gravity.

6. What is the acceleration due to gravity on the surface of the Earth?

   • Answer: The acceleration due to gravity on the surface of the Earth is approximately $9.8 \, \text{m/s}^2$.

7. How does the gravitational force between two objects depend on their masses?

   • Answer: The gravitational force between two objects is directly proportional to the product of their masses. If either mass increases, the gravitational force increases proportionally.

8. Why do astronauts experience weightlessness in space?

   • Answer: Astronauts experience weightlessness because they are in a state of free fall while orbiting Earth. Both they and their spacecraft are accelerating towards Earth at the same rate due to gravity, so they do not feel the force of gravity in the same way as they would on the surface.

9. What is the gravitational force between two 1 kg masses separated by a distance of 1 meter?

   • Answer: Using the formula $F = G \frac{m_1 m_2}{r^2}$, where $G = 6.674 \times 10^{-11} \, \text{N m}^2 \text{kg}^{-2}$, $m_1 = 1 \, \text{kg}$, $m_2 = 1 \, \text{kg}$, and $r = 1 \, \text{m}$, the gravitational force is $F = 6.674 \times 10^{-11} \, \text{N}$.

10. How does the gravitational force between two objects change if their masses are both tripled?

    • Answer: If both masses are tripled, the gravitational force becomes nine times greater, because the force is directly proportional to the product of the masses ($F \propto m_1 m_2$).

11. What is the relation between gravitational force and distance between two objects?

    • Answer: The gravitational force is inversely proportional to the square of the distance between the centers of two objects. As distance increases, the force decreases rapidly.

12. Why does the Moon not fall into the Earth despite being under the influence of Earth's gravity?

    • Answer: The Moon is in constant free fall towards Earth, but it also has a tangential velocity that causes it to orbit Earth rather than falling straight into it. This balance of forces results in the Moon's stable orbit.

13. Explain how gravity affects the trajectory of a projectile.

    • Answer: Gravity pulls a projectile downward, causing its path to curve. The projectile follows a parabolic trajectory due to the constant downward force of gravity.

14. What is escape velocity?

    • Answer: Escape velocity is the minimum velocity an object needs to break free from the gravitational influence of a celestial body without further propulsion. For Earth, it is approximately $11.2 \, \text{km/s}$.

15. How does the gravitational force between two objects change if the distance between them is halved?

    • Answer: If the distance between two objects is halved, the gravitational force becomes four times greater, as the force is inversely proportional to the square of the distance.

16. What role does gravity play in the formation of planets and stars?

    • Answer: Gravity causes gas and dust in space to clump together, forming larger bodies like planets and stars. It pulls material together, leading to the formation of these celestial objects.

17. Describe the effect of gravity on a satellite in orbit around Earth.

    • Answer: A satellite in orbit around Earth is constantly falling towards Earth due to gravity, but its forward velocity ensures that it keeps missing Earth. This results in a stable orbit.

18. How does gravitational force vary with altitude?

    • Answer: As altitude increases, the distance from the Earth's center increases, which causes the gravitational force to decrease. The force decreases with the square of the distance from the Earth's center.

19. What is the gravitational force between two objects of masses 10 kg and 15 kg separated by a distance of 2 meters?

    • Answer: Using the formula $F = G \frac{m_1 m_2}{r^2}$, with $G = 6.674 \times 10^{-11} \, \text{N m}^2 \text{kg}^{-2}$, $m_1 = 10 \, \text{kg}$, $m_2 = 15 \, \text{kg}$, and $r = 2 \, \text{m}$, the gravitational force is $F = 6.674 \times 10^{-11} \times \frac{10 \times 15}{2^2} = 5.006 \times 10^{-10} \, \text{N}$.

20. Explain the concept of gravitational field strength.

    • Answer: Gravitational field strength at a point is the force per unit mass experienced by a small test mass placed at that point. It is given by $g = \frac{F}{m}$, where $g$ is the gravitational field strength, $F$ is the gravitational force, and $m$ is the mass of the test object.

These questions and answers should give you a thorough understanding of the key concepts in the topic of Gravitation for Class 9 Science