Gravitation

Written by Dr. Hamza Farooq (Physics)

Class 9 · Physics · 10 questions

Name: ____________________ Date: ____________

Newton's law of gravitation says the force between two masses is proportional to:
- A The sum of the masses
- B The difference of the masses
- C The distance between them
- D The product of the masses
If the distance between two masses is doubled, the gravitational force becomes:
- A Four times
- B One quarter
- C Half
- D Double
The value of g near the surface of the Earth is about:
- A 0.98 m/s²
- B 98 m/s²
- C 9.8 m/s²
- D 6.67 m/s²
The acceleration due to gravity on the Moon compared with Earth is about:
- A Six times greater
- B Zero
- C One sixth
- D The same
A satellite stays in orbit around the Earth because:
- A It is very light
- B It has no weight
- C Gravity provides the centripetal force
- D There is no gravity in space
The mass of a body on the Moon compared with its mass on Earth is:
- A More
- B The same
- C Less
- D Zero
The gravitational force between two bodies is always:
- A Repulsive
- B Zero
- C Alternating
- D Attractive
The value of the gravitational constant G is about:
- A 3 x 10⁸ N m²/kg²
- B 6.67 x 10⁻¹¹ N m²/kg²
- C 9.8 N m²/kg²
- D 6.67 N m²/kg²
An astronaut in orbit feels weightless because:
- A Her mass is zero
- B Air pushes her up
- C She is in free fall around the Earth
- D There is no gravity
The orbital speed of a satellite depends on:
- A Its shape
- B The mass of the Earth and the orbit radius
- C The mass of the satellite only
- D Its colour

Answer key

1. D, 2. B, 3. C, 4. C, 5. C, 6. B, 7. D, 8. B, 9. C, 10. B

F = G m₁ m₂ / d², so the force is proportional to the product of the masses.
F is proportional to 1 / d². Doubling d makes the force one quarter.
The acceleration due to gravity near Earth's surface is about 9.8 m/s².
The Moon has less mass, so g there is about one sixth of the value on Earth.
Gravity pulls the satellite towards the Earth and acts as the centripetal force that keeps it on a curved path.
Mass is the amount of matter and does not change with place. Only weight changes.
Gravity only attracts.
G = 6.67 x 10⁻¹¹ N m²/kg².
The astronaut and spacecraft fall together.
v = square root of (G M / r).