Question

Suppose a planet has a mean distance from the sun, 4 times that of earth's. How many earth years will this planet take to orbit the sun?

• A. 64 Earth years
• B. 8 Earth years
• C. 4 Earth years
• D. 32 Earth years

Answer 1

The correct option is B 8 Earth years

From kepler's third law, the time of revolution of a planet and the distance from the star is related by the following relation.
$T^2\propto R^3$
Therefore $\frac{T_1^2}{R_1^3}=\frac{T_2^2}{R_2^3}$
For the given question, $R_1=R_{e}and{R}_2=4R_e,$ then
$\frac{1}{R_e^3}=\frac{T_2^2}{(4R_e{)}^3}$
$T_2^2=64$
$T_2=8$
Therefore, it would take 8 years for this planet to revolve around the sun.