Find Pluto's year length using Kepler's third law.

[D.J Falcon]

Homework Statement

Pluto is 40 times further from the Sun than we are. How long is a year on Pluto? (Use Kepler's third law.)

Homework Equations

4∏^2/Gm=T^2/r^3

The Attempt at a Solution

Te^2(Earth period)=x*r^3

Tp^2(Pluto period)=x*(40r)^3


I don't know what to do exactly from here. I'm not even entirely sure that I'm going about this the right way.

Any help would be appreciated.

 

[estro]

Hint: For every planet [which goes around the sun] in our solar system R^3/T^2=constant.
Why?

 

[D.J Falcon]

Hint: For every planet [which goes around the sun] in our solar system R^3/T^2=constant.
Why?

I've already made x a constant (T^2/r^3), in the attempt at a solution. I just don't realize what to do from there.

 

[estro]

I don't know what you mean by:

I've already made x a constant (T^2/r^3), in the attempt at a solution.
...

First of all you need to understand why for every planet which goes around the same star R^3/T^2 is constant.
Then don't forget what you already know about the difference in R between Earth and Pluto.

I'm already gave you the answer, actually...