Gravitation (Class 9 Science)

Gravitation is the force of attraction between all objects in the universe, discovered and explained by Newton. Understanding gravity is essential for unde

Gravitation (Class 9 Science)

Gravitation is the force of attraction between all objects in the universe, discovered and explained by Newton. Understanding gravity is essential for unde

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TL;DR: Gravitation is the force of attraction between all objects in the universe, discovered and explained by Newton. Understanding gravity is essential for…

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Gravitation is the force of attraction between all objects in the universe, discovered and explained by Newton. Understanding gravity is essential for unde

Gravitation MCQs with Answers & Explanations

Q1. Newton's law of universal gravitation states that the gravitational force between two objects is:

  1. Directly proportional to the sum of their masses
  2. Directly proportional to the distance between them
  3. Independent of their masses
  4. Inversely proportional to the square of distance between them ✓ (correct)

Explanation: The gravitational force is directly proportional to the product of masses and inversely proportional to the square of distance: F = GMm/r^2.

Q2. The gravitational constant G is approximately:

  1. 6.67 x 10^-11 N m^2/kg^2 ✓ (correct)
  2. 9.8 m/s^2
  3. 10^-11 N/kg
  4. 6.67 x 10^11 N m^2/kg^2

Explanation: The gravitational constant G equals 6.67 x 10^-11 N m^2/kg^2.

Q3. The weight of an object is:

  1. The amount of matter in the object
  2. The gravitational force exerted on the object ✓ (correct)
  3. Independent of mass
  4. The same everywhere

Explanation: Weight is the force of gravity acting on an object and equals mass times gravitational acceleration (W = mg).

Q4. Acceleration due to gravity at Earth's surface is approximately:

  1. 10 m/s^2
  2. 6.67 m/s^2
  3. 9.8 m/s^2 ✓ (correct)
  4. 15 m/s^2

Explanation: The acceleration due to gravity near Earth's surface is approximately 9.8 m/s^2 or 10 m/s^2.

Q5. If the mass of an object is doubled, its weight becomes:

  1. Quarter
  2. Half
  3. Same
  4. Double ✓ (correct)

Explanation: Weight = mg, so if mass doubles, weight also doubles (assuming g remains constant).

Q6. An astronaut weighs 100 N on Earth. On the Moon, where g = 1.6 m/s^2, the astronaut's weight would be approximately:

  1. 16 N ✓ (correct)
  2. 100 N
  3. 1000 N
  4. 60 N

Explanation: Weight 100 N on Earth (g = 10 m/s²) gives mass = 100/10 = 10 kg. Mass does not change, so on the Moon W = m x g = 10 x 1.6 = 16 N.

Q7. The orbital velocity of a satellite depends on:

  1. The radius of orbit
  2. Only the planet's mass and radius of orbit ✓ (correct)
  3. Both mass and radius of orbit
  4. Its mass

Explanation: Orbital velocity depends on the mass of the central body and the orbital radius, not on the satellite's mass.

Q8. Free fall is a motion where:

  1. Velocity is constant
  2. Resistance is maximum
  3. Only gravitational force acts ✓ (correct)
  4. No force acts

Explanation: Free fall is motion under gravity alone, where only the gravitational force acts on the object.

Q9. If the distance between two objects is doubled, the gravitational force becomes:

  1. Four times
  2. Double
  3. Half
  4. One-fourth ✓ (correct)

Explanation: Since F ∝ 1/r^2, doubling distance makes force 1/4 of the original.

Q10. Mass is different from weight because:

  1. Mass is matter quantity, weight is gravitational force ✓ (correct)
  2. Mass changes with location
  3. Weight is constant everywhere
  4. They have the same definition

Explanation: Mass is the quantity of matter and is constant everywhere, while weight is the gravitational force and varies with location.

Frequently Asked Questions

Why do objects fall at the same rate on Earth regardless of their mass?

Acceleration due to gravity is constant (9.8 m/s^2) for all objects near Earth's surface, independent of their mass.

How does gravity work in space where there is no air resistance?

Gravity acts on objects regardless of the medium, causing them to accelerate toward the massive body due to gravitational force.

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