Gravitation
Universal gravitation, orbital motion, escape velocity
Key Concepts
- Kepler's 1st law: planets move in ellipses with sun at one focus
- Kepler's 2nd law: equal areas are swept in equal times (L conserved)
- Kepler's 3rd law: T² ∝ r³
- Gravitational field is zero at centre of a uniform spherical shell
- g decreases both above and below Earth's surface
Important Formulae
| Gravitational force | F = Gm₁m₂/r² |
| Surface gravity | g = GM/R² |
| Escape velocity | v_esc = √(2GM/R) = √(2gR) |
| Orbital velocity | v_orb = √(GM/r) |
| Orbital period | T = 2πr/v_orb |
| g at height h | g_h = g(1 − 2h/R) for h ≪ R |
Quick Tips
- Escape velocity ≈ 11.2 km/s for Earth; orbital velocity for near-orbit ≈ 7.9 km/s.
- Geostationary orbit: T = 24 h, height ≈ 36,000 km above equator.
- Gravitational PE = −GMm/r (negative because bound system).
Sample Practice Questions
-
Kepler's second law states that the line joining planet and sun sweeps equal areas in:
Show answer
Answer: Equal time intervals
-
The gravitational potential at Earth's centre (surface potential = V₀):
Show answer
Answer: -3V₀/2
-
A satellite in circular orbit has total energy:
Show answer
Answer: -GMm/2r
-
Intensity of gravitational field at a point is:
Show answer
Answer: Force per unit mass
Practice Questions
Practice 20 randomly selected NEET questions on Gravitation. Answers are revealed after each question.
Start Practice →Frequently Asked Questions
What are the key concepts in Gravitation for NEET?
Kepler's 1st law: planets move in ellipses with sun at one focus; Kepler's 2nd law: equal areas are swept in equal times (L conserved); Kepler's 3rd law: T² ∝ r³; Gravitational field is zero at centre of a uniform spherical shell; g decreases both above and below Earth's surface.
Which formulae are important for Gravitation in NEET?
Gravitational force: F = Gm₁m₂/r²; Surface gravity: g = GM/R²; Escape velocity: v_esc = √(2GM/R) = √(2gR); Orbital velocity: v_orb = √(GM/r); Orbital period: T = 2πr/v_orb; g at height h: g_h = g(1 − 2h/R) for h ≪ R.
How can I practise NEET Gravitation questions for free?
Practise free NEET Gravitation questions with instant answers and explanations on Safe Learning for Kids — no sign-up required.