Question

Assertion :The smaller the orbit of a planet around the Sun, the shorter is the time it takes to complete. Reason: According to Kepler's third law of planetary motion, square of time period is proportional to cube of mean distance from Sun.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Third law of Kepler states that square of time period of a planet is proportional to the cube of semi major axis of the ellipse.

According to Kepler's third law of planetory motion, the square of the time period of a planet about the Sun is proportional to the cube of the semi-major axis of the ellipse or mean distance of the planet from the Sun, i.e., $T^2\propto a^3$.

When $a$ is smaller, the time period is shorter.