Planet Velocity at Aphelion: Find the Answer

[Ready2GoXtr]

Homework Statement

At perihelion a planet in another solary system is 175 x 10 ^ 6km from its Sun and is traveling at 40km/s. At aphelion it 250 x 10 ^ 6 km distant and is traveling at?

Homework Equations

IiWi = IfWf

The Attempt at a Solution

What do i do?

 

[Dick]

Use conservation of angular momentum as you are trying to do. What are I and W in terms of mass m, velocity v and radius r of the planet?