Question

The radius of a planet is 4 times the radius of the earth. The time period of revolution of the planet will be:

• A. 1 yr
• B. 2 yr
• C. 4 yr
• D. 8 yr

Answer 1

The correct option is D 8 yr

According to Kepler's law
$T^2\alpha R^3\to \left(I\right)$
Now,
$R_1=4R$
So, $T_1^2\alpha R_1^3$
$T_1^2\alpha 64R^3\to \left(II\right)$
on dividing both equations, we get,
$\frac{T^2}{T_1^2}=\frac{1}{64}$
$T_1=8T$
i.e, It will take 8 years to complete a revolution.