Answer: Conservation of angular momentum.
- A Conservation of energy
- B Conservation of angular momentum
- C Conservation of linear momentum
- D Newton's third law
Correct answer: B. Conservation of angular momentum
Explanation: Equal areas swept in equal time means angular momentum is constant: a result of no torque acting on the planet.
g is maximum at Earth's surface; going up, it falls off as 1/r² (inverse-square); going down, it falls off linearly with depth (since only the mass enclosed within radius r contributes), reaching zero at the centre.
Concept context
Universal gravitation, orbital mechanics, gravitational potential, and escape velocity.