How would you calculate the length of a year on a planet?

[songminho]

Homework Statement

How would you calculate the length of a year in Earth years on a hypothetical planet? (given the mass + radius of the planet)

I understand Kelper's law is used somehow, but is orbital velocity needed?

 

[rude man]

Try Law #3, "The Law of the Periods".
The radius of the planet is a no-count. So is the mass.

 

[J Hann]

You can start with: gravitational attraction = centripetal force
G M m / R^2 = m v^2 / R
I assume that by radius is meant the radius (mean) of the planet's orbit.
Note that the period can then be calculated in terms of v and R.