Q.

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             [2025]

1 172 earth days  
2 124 earth days  
3 88 earth days  
4 225 earth days  

Ans.

(3)

Given, Rmartian=4Rmercury

Tmartian=687 Earth days

Tmercury= ?

By Kepler's Third Law

(TMercuryTMartian)2=(RMercuryRMartian)3=(14)3=164

TMercury=TMartian8=6878=85.8 days

Nearest answer is 88 Earth days.