Q 11-07-004NEETNEET 2025Top questionEasy
The radius of Martian orbit around the Sun is about $4$ times the radius of the orbit of Mercury. The Martian year is $687$ Earth days. Then which of the following is the length of $1$ year on Mercury ?
Answer: (A) $88$ earth days
Concept. Kepler's third law: $T \propto r^{3/2}$.
Step 1. Scale. $T_{\text{Mercury}} = 687 \times \left(\dfrac14\right)^{3/2} = \dfrac{687}{8} \approx 86$ days; the closest option is $88$.
Answer. $88$ earth days (Option A).
Solution by Sreeraj P, M.Sc Physics