Gravitation — Class 9 MCQs with Answers

Gravitation — important questions & MCQs with answers (Class 9 Science)

14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.

1. Q1Easy

   The universal gravitational constant G has the value approximately:

   A.9.8 m/s²

   B.6.67 × 10⁻¹¹ N·m²/kg²✓ Correct

   C.3 × 10⁸ m/s

   D.1.6 × 10⁻¹⁹ C

   Answer: B. 6.67 × 10⁻¹¹ N·m²/kg²

   Explanation: G is Newton's gravitational constant, about 6.674 × 10⁻¹¹ N·m²/kg² — the same everywhere in the universe, unlike g (9.8 m/s²), which varies by planet.

2. Q2Easy

   Acceleration due to gravity (g) on Earth's surface is approximately:

   A.9.8 m/s²✓ Correct

   B.6.67 m/s²

   C.10⁸ m/s²

   D.6.4 × 10⁶ m/s²

   Answer: A. 9.8 m/s²

   Explanation: g, the acceleration due to gravity near Earth's surface, is about 9.8 m/s²; it's often rounded to 10 m/s² for quick calculations.

3. Q3Easy

   The upward force exerted by a fluid on an immersed body is called:

   A.Gravitational force

   B.Normal force

   C.Frictional force

   D.Buoyant force✓ Correct

   Answer: D. Buoyant force

   Explanation: When a body is immersed in a fluid, the fluid pushes back with an upward buoyant (upthrust) force — this is what lets objects float or feel lighter.

4. Q4Easy

   The universal law of gravitation was proposed by:

   A.Newton✓ Correct

   B.Einstein

   C.Galileo

   D.Kepler

   Answer: A. Newton

   Explanation: Sir Isaac Newton proposed the universal law of gravitation in 1687 — the same force pulling an apple down also keeps the Moon in orbit.

5. Q5Easy

   Mass and weight differ in that:

   A.Mass is a force; weight is matter

   B.They are the same

   C.Mass is constant; weight changes with location✓ Correct

   D.Mass is in newtons

   Answer: C. Mass is constant; weight changes with location

   Explanation: Mass (kg) is fixed matter in a body. Weight = mg (N) depends on gravity, so the same body weighs less on the Moon though its mass stays unchanged.

6. Q6Easy

   The SI unit of density is:

   A.g/cm²

   B.kg/m³✓ Correct

   C.N/m²

   D.kg·m³

   Answer: B. kg/m³

   Explanation: Density = mass ÷ volume, so its SI unit is kg/m³. Water's density, for example, is 1000 kg/m³, or equivalently 1 g/cm³.

7. Q7Medium

   Newton's universal law of gravitation: F =

   A.G m₁ m₂ / r²✓ Correct

   B.G m₁ m₂ / r

   C.G (m₁ + m₂) / r²

   D.G m₁ m₂ × r²

   Answer: A. G m₁ m₂ / r²

   Explanation: Newton's law of gravitation: F = Gm₁m₂/r² — force is inversely proportional to the SQUARE of the distance, not just the distance itself.

8. Q8Medium

   Weight of a 5 kg body on Earth (g = 9.8) =

   A.5 N

   B.50 N

   C.15 N

   D.49 N✓ Correct

   Answer: D. 49 N

   Explanation: Weight = mg = 5 kg × 9.8 m/s² = 49 N. A common slip is reporting the mass value (5) itself as the weight instead of multiplying by g.

9. Q9Medium

   Archimedes' principle states that the buoyant force on a body in fluid equals:

   A.The weight of fluid displaced✓ Correct

   B.The weight of the body

   C.The volume of fluid

   D.Density × volume × velocity

   Answer: A. The weight of fluid displaced

   Explanation: Archimedes' principle: buoyant force on a submerged body equals the weight of the fluid it displaces — not the body's own weight or the fluid's volume alone.

10. Q10Medium

    Two 1 kg masses 1 m apart attract each other with force F. If both masses are doubled, F becomes:

    A.2F

    B.4F✓ Correct

    C.F/2

    D.F

    Answer: B. 4F

    Explanation: F ∝ m₁m₂, so doubling BOTH masses multiplies the product by 2 × 2 = 4, making the new force 4F — treating each doubling as adding gives the wrong answer, 2F.

11. Q11Medium

    A stone is dropped from rest. Its velocity after 2 s (g = 10 m/s²) is:

    A.5 m/s

    B.10 m/s

    C.40 m/s

    D.20 m/s✓ Correct

    Answer: D. 20 m/s

    Explanation: Starting from rest, v = u + gt = 0 + 10 × 2 = 20 m/s. Each second under g = 10 m/s² adds another 10 m/s of speed.

12. Q12Hard

    If the distance between two masses is doubled, gravitational force becomes:

    A.One-fourth✓ Correct

    B.Half

    C.Doubled

    D.Quadrupled

    Answer: A. One-fourth

    Explanation: By F ∝ 1/r², doubling the distance means dividing by r² = 2² = 4, so force drops to F/4 — a common mistake is halving the force instead of squaring the distance change.

13. Q13Hard

    On the Moon, where g ≈ 1.6 m/s², a 60 kg person weighs:

    A.60 N

    B.588 N

    C.96 N✓ Correct

    D.600 N

    Answer: C. 96 N

    Explanation: Weight = mg = 60 kg × 1.6 m/s² = 96 N on the Moon, far less than the same person's Earth weight (60 × 9.8 = 588 N) — mass stays 60 kg in both places; only weight changes.

14. Q14Hard

    A block of relative density 0.6 is placed in water. The fraction of the block submerged is:

    A.0.4

    B.1.0

    C.0.6✓ Correct

    D.0.06

    Answer: C. 0.6

    Explanation: For a floating body, the submerged fraction equals its relative density: V_submerged/V = ρ_body/ρ_water = 0.6/1.0 = 0.6, so 60% stays underwater.

Gravitation — FAQs

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