Question 15: Planetary Orbits and Conservation Laws – Rankers Physics

Keplers Law: Practice Problem & Solution

Assertion (A): When planet moves in elliptical orbit around Sun. Its angular momentum about sun remains conserved. Reason (R): Total mechanical energy of planet - sun system remains conserved.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Keplers Law. Understanding the underlying formula is key to arriving at the correct answer below:

Assertion (A) is true. Gravitational force is a central force, so the torque about the Sun is zero, leading to angular momentum conservation. Reason (R) is also true. Gravitational force is conservative, so total mechanical energy of the system is conserved. However, energy conservation does not explain angular momentum conservation, as they are distinct conservation laws.

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