Question

A planet of the sun is in a circular orbit around the sun, midway between the sun and the earth. Then

• A. the period of the planet is nearly $229days$
• B. the period of the planet is nearly $129days$
• C. the speed of the planet is greater than the escape velocity of the earth
• D. the acceleration of the planet is two times the acceleration of the earth

Answer 1

Answer: (B)

$T^2\propto r^3$
$\frac{T_1}{T_2}={\left(\frac{r}{r/2}\right)}^{3/2}$
$\frac{365\text{days}}{T}=2\sqrt{2};T=\frac{365}{2\sqrt{2}}\text{days}\Rightarrow 129\text{days}$