Gravitation — Previous Year Questions (Class 9 Science)
Gravitation is the force of attraction between any two masses. Learn Newton's law of universal gravitation, weight, and orbital motion.
TL;DR: Gravitation is the force of attraction between any two masses. Learn Newton's law of universal gravitation, weight, and orbital motion.
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Gravitation is the force of attraction between any two masses. Learn Newton's law of universal gravitation, weight, and orbital motion.
Gravitation — Previous Year Questions with Solutions
Q (2023, 3 marks): State Newton's law of universal gravitation and write its mathematical form.
Answer: Newton's Law of Universal Gravitation: Every object in the universe attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.
Mathematical form: F = G(m1 × m2) / r²
Where:
F = gravitational force (N)
G = gravitational constant = 6.67 × 10^-11 Nm²/kg²
m1, m2 = masses of objects (kg)
r = distance between centers of mass (m)
Q (2022, 2 marks): Calculate the gravitational force between two objects of masses 2 kg and 3 kg placed 1 m apart.
Answer: Using F = G(m1 × m2) / r²
F = (6.67 × 10^-11)(2 × 3) / (1)²
F = (6.67 × 10^-11)(6) / 1
F = 40.02 × 10^-11 N
F = 4.002 × 10^-10 N
Q (2023, 3 marks): Explain the difference between mass and weight. What is the relation between them?
Answer: Mass:
- Quantity of matter in an object
- Measured in kg
- Same everywhere (constant)
- Scalar quantity
- Measured using balance
Weight:
- Force due to gravity on an object
- Measured in Newton (N)
- Varies with location (depends on g)
- Vector quantity
- Measured using spring balance
Relation: W = mg
Where W = weight, m = mass, g = acceleration due to gravity (9.8 m/s² on Earth)
Q (2021, 2 marks): The value of g on Moon is 1/6 of that on Earth. If a person's mass is 60 kg, find their weight on Moon. (g on Earth = 10 m/s²)
Answer: g on Earth = 10 m/s²
g on Moon = 10/6 = 5/3 m/s²
Mass m = 60 kg
Weight on Moon = mg = 60 × (5/3) = 100 N
Note: Weight on Earth = 60 × 10 = 600 N
So weight on Moon is 1/6 of weight on Earth
Q (2022, 3 marks): Explain why satellites don't fall to Earth even though they are pulled by Earth's gravity.
Answer: Satellites don't fall because:
1. They are in orbital motion (continuous circular/elliptical path)
2. Gravitational force provides the centripetal force needed
3. The satellite's velocity is such that gravitational pull equals centripetal force requirement
4. This creates equilibrium, keeping satellite in orbit
5. Orbital velocity for low Earth orbit ≈ 7.8 km/s
Formula: GMm/r² = mv²/r
where GM/r = v²
If velocity decreases, satellite falls; if too fast, it escapes
Q (2023, 2 marks): If the distance between two objects is doubled, how does the gravitational force change?
Answer: Original force: F1 = G(m1 × m2) / r²
New distance = 2r
New force: F2 = G(m1 × m2) / (2r)² = G(m1 × m2) / 4r²
F2 / F1 = [G(m1 × m2) / 4r²] / [G(m1 × m2) / r²]
F2 / F1 = 1/4
Therefore: F2 = F1/4
The gravitational force becomes 1/4 of original (decreases by factor of 4)
Frequently Asked Questions
What is acceleration due to gravity and what is its value?
Acceleration due to gravity (g) is the acceleration acquired by a freely falling object under gravity alone. Its value is approximately 9.8 m/s² on Earth's surface (often rounded to 10 m/s²). It varies slightly with latitude and altitude, being higher at poles and lower at equator.
What is the difference between gravitational potential energy and kinetic energy?
Gravitational PE (mgh) is energy due to position relative to Earth. Kinetic energy (1/2 mv²) is energy due to motion. As an object falls, PE decreases and KE increases, with total mechanical energy conserved (ignoring friction).
More Class 9 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Acids, Bases and Salts
- Metals and Non-metals
- Life Processes
🤖 Stuck on any of these? Ask Syllab's free AI Tutor to explain step by step →