# Comet's Velocity

1. Oct 21, 2007

### Jtappan

1. The problem statement, all variables and given/known data

The orbit of Halley's Comet around the Sun is a long thin ellipse. At its aphelion (point farthest from the Sun), the comet is 5.7 * 10^12 m from the Sun and moves with a speed of 11.0 km/s. What is the comet's speed at its perihelion (closest approach to the Sun) where its distance from the Sun is 8.4 * 10^10 m?
_____km/s

2. Relevant equations

PEi+KEi=PEf+KEf

3. The attempt at a solution

do the m and g values cancel out when doing this because they are not given? Im totally lost...

2. Oct 22, 2007

### Mindscrape

Weak, they gave you the perihelion. Since they gave perihelion distance, a lot of trouble is saved. Now this begs the question of what is the difference between the aphelion and the perihelion? Is there any kind of easily attainable relation you can use? To give you a hint, you might want to consider more than energy conservation. (Hint hint: one of them types of momentum, and one is better than the other.)

Did you know that you can solve for the perihelion with the information they have given you? If you feel ambitious, give it a try.

3. Jul 4, 2008