# Homework Help: Energy needed for pluto to escape earth surface

1. Dec 30, 2007

### jperk980

Calculate the amount of energy required to escape from the surface of the following bodies, relative to that required to escape from the surface of Earth.(a) Pluto

I keep on getting the same answer to be .011092137 but according to the website i am working on that is not correct. I used the mass of earth to be 5.98e24, mass of Pluto is .002*5.98e24 and the radius's of earth is 6.378e6 and Pluto is 1.15e6. I understand that (Mp*Re)/(Me*Rp) should be the correct formula.

If you get a different answer please help me achieve the answer you got because i have been trying many different solutions and still have not been able to figure out the question. I have a 5% grace period which all answers within 5% are correct.
Thank you

2. Dec 30, 2007

### Staff: Mentor

3. Dec 30, 2007

### belliott4488

This is the correct formula for what? Ratio of velocities? I don't think so.

Where did you get this expression, and can you derive it? You should be able to, if you want to understand the problem completely. Try doing that, and I think you'll see what you need to do to correct the expression that you gave above. If you're not sure how to do that, just ask.

4. Dec 30, 2007

### belliott4488

oops. We crossed responses.

Are you sure he's correct? For ratio of escape velocities? KE is proportional to v^2 and PE is proportional to M/R, right? Unless I missed a radical sign somewhere, that's not what I get ...

5. Dec 30, 2007

### Staff: Mentor

The question asked for energy, not velocity:

6. Dec 30, 2007

### Bright

In original post the question is about energy, not velocity

7. Dec 30, 2007

### belliott4488

aughh! SORRY!!! I mis-read it, as you've noticed ... and I keep crossing messages.

Never mind me!

(except that I now agree with jperk's original answer)