# Elliptical orbit question

1. Mar 23, 2010

### superaznnerd

elliptical orbit question plz help

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

2. Relevant equations
2a (average distance of satellite from central body) = A (aphelium) + P (perihelium)
ME = KE + PE
ME = -GMm/24
KE = .5mv^2
PE = -GMm/r
ME orignall = ME final
3. The attempt at a solution
I tried to put ME = KE + PE = constant.
I solved for theoretical A, and P, if the velocity was only transverse.
Then, I subtracted the theoretical P by the distance caused by the KE. I sitll did not get the answer htough

#### Attached Files:

• ###### ellipt orbit.jpg
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Last edited: Mar 23, 2010
2. Mar 23, 2010

### nickjer

Re: elliptical orbit question plz help

Please list all of the formulas and steps you did. Not sure what you are defining as A and P.

3. Mar 23, 2010

### superaznnerd

Re: elliptical orbit question plz help

anyone?

4. Mar 23, 2010

### passingthru

Re: elliptical orbit question plz help

Given the components of the velocity, can you determine the angle at that point? What is the polar equation for an ellipse in terms of the eccentricity?

5. Mar 23, 2010

### nickjer

Re: elliptical orbit question plz help

There is a formula for eccentricity in terms of energy and angular momentum. If you don't know it, then you will have to solve for it using the conservation of energy and the conservation of angular momentum.

6. Mar 23, 2010

### superaznnerd

Re: elliptical orbit question plz help

I looked at the wiki page, and have no clue hwo to apply conservation of angular momentum. could someone please show me how to do it?

7. Mar 23, 2010

### nickjer

Re: elliptical orbit question plz help

Calculate the angular momentum of the satellite using

$$\vec{L} = m\vec{r}\times \vec{v}$$

8. Mar 23, 2010

### D H

Staff Emeritus
Re: elliptical orbit question plz help

Don't even bother with the satellite mass. It's just going to divide out in the end. Just use specific energy and specific angular momentum.

Which wiki page? There are several of them.

No, we can't show you how to do it. That would be cheating.

9. Mar 29, 2010

### passingthru

Re: elliptical orbit question plz help

Can you look up the polar form of the equation for an ellipse, in terms of r, $\theta$, and the eccentricity? Can you find the angle, given the components of the velocity?

10. Mar 29, 2010

### nickjer

Re: elliptical orbit question plz help

The polar form of an ellipse has two unknowns: 'a' and eccentricity. So it won't be enough to solve for the eccentricity alone.

11. Mar 29, 2010

### D H

Staff Emeritus
Re: elliptical orbit question plz help

I think the original poster has moved on by now.

The sad thing is that the word "eccentricity" is in big bold letters in the attachment in the original post. The OP claims to have "read the wiki page". Which one, I don't know. The wiki page on "Eccentricity" is a redirection page, and one of the redirects is to "Orbital eccentricity". The first equation specifies how to solve this exact problem in general; the third equation specializes this first equation to gravitation. In other words, exactly what the OP needed to use to solve this problem is right there, right up front, on "the wiki page".