Question

$\text{Assertion}$: Kepler's laws of planetary motion are a consequence of Newton's law of gravitation.

$\text{Reason}$: Kepler's laws can be derived using Newton's law of gravitation.

• A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
• B. Both assertion and Reason are true, but Reason is not the correct explanation of Assertion.
• C. Assertion is true, but Reason is false.
• D. Assertion is false, but Reason is true.

Answer 1

The correct option is A Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Kepler’s laws are a direct consequence of Newton’s laws of gravitation.

Planet’s elliptical orbit is a consequence of the inverse square law.

Kepler’s second law i.e. constant areal velocity is a consequence of conservation of angular momentum as we can assume the planet and the star to be concentrated at their centers for the calculation of gravitational force.

The law of periods is a consequence of the elliptical orbit.

Why this question: To make students understand the physics behind Kepler’s laws, which was purely observational when it came into existence. Takeaway: If the nature of gravitational force or inverse square law changes, then Kepler’s laws will not be valid or will have to be modified.