Which of the following quantities remains conserved when an object moves under the gravitational pull of another object?
Show answer & explanation
Correct answer: D
Explanation
Answer: Angular momentum and mechanical energy
Explanation: When an object moves under the influence of gravitational force alone (a conservative central force), certain physical quantities remain conserved. In such motion, both angular momentum and mechanical energy (sum of kinetic and potential energy) remain constant.
This is because gravitational force acts along the line joining the two masses, producing no external torque about the center, hence conserving angular momentum. Also, since gravity is a conservative force, mechanical energy remains conserved.
Additional Key Points:
Conservation of angular momentum is due to zero external torque.
Mechanical energy = Kinetic energy + Potential energy.
This principle explains planetary motion and satellite orbits.
Kepler’s laws of planetary motion are based on these conservation principles.
Potential Exam-Oriented Questions & Answers:
Question: What is mechanical energy?
Answer: Sum of kinetic energy and potential energy
Question: Which laws of planetary motion are based on conservation principles?
Answer: Kepler’s laws