JEE · Physics · Gravitation doubts

What does “Universal law of gravitation” actually mean in Gravitation, and why does it matter for JEE?

every two masses attract with F = G·m₁m₂/r² along the line joining them.

I keep getting “Universal law of gravitation” questions wrong in Gravitation. What's the trap?

forgetting the force depends on 1/r² — doubling the distance quarters the force.

What does “Acceleration due to gravity g” actually mean in Gravitation, and why does it matter for JEE?

g = GM/R² at a planet's surface; it decreases with both altitude and depth.

I keep getting “Acceleration due to gravity g” questions wrong in Gravitation. What's the trap?

treating g as a fixed 9.8 everywhere, including in orbit.

What does “Gravitational potential energy” actually mean in Gravitation, and why does it matter for JEE?

for large distances PE = −GMm/r (negative, zero at infinity), not mgh.

I keep getting “Gravitational potential energy” questions wrong in Gravitation. What's the trap?

using mgh far from the surface, where it no longer holds.

What does “Escape velocity” actually mean in Gravitation, and why does it matter for JEE?

the minimum speed to leave a planet's gravity, v = √(2GM/R) ≈ 11.2 km/s for Earth.

I keep getting “Escape velocity” questions wrong in Gravitation. What's the trap?

confusing it with orbital velocity.

What does “Kepler's laws” actually mean in Gravitation, and why does it matter for JEE?

orbits are ellipses; a planet sweeps equal areas in equal times; T² ∝ r³.

I keep getting “Kepler's laws” questions wrong in Gravitation. What's the trap?

assuming orbital speed is constant — planets move faster near the Sun.

What is the difference between orbital velocity and escape velocity?

Orbital velocity keeps a satellite in a circular orbit; escape velocity (√2 times larger) lets it leave gravity forever.

What is the difference between g at height and g at depth?

Above the surface g ∝ 1/(R+h)²; below the surface g decreases roughly linearly to zero at the centre.

What is the difference between weight and gravitational force?

Weight is the gravitational force experienced (mg); in free fall the sensation of weight vanishes even though gravity still acts.

When do I use F = G m₁m₂/r² in Gravitation, and what does it mean?

the gravitational force between two masses.