A planet goes round the sun three times as fast as the earth. If `r_(p) and r_(e)` are the radii of orbit of the planet and the earth respectively then

Options

A. `r_(e)^(3) = 8 r_(p)^(3)`
B. `r_(e)^(3) = 3 r_(p)^(3)`
C. `r_(e)^(3) = 9 r_(p)^(3)`
D. `r_(e)^(3) = (1)/(3) r_(p)^(3)`

Answer

C

Explanation

`(T_(p))/(T_(e)) = (1)/(3)`
`((T_(p))/(T_(e)))^(2) = ((r_(p))/(r_(e)))^(3) rArr r_(e)^(3) = 9r_(p)^(3)`