# Homework Help: Kinetic energy of space probe problem

1. Apr 22, 2007

### chouZ

1. The problem statement, all variables and given/known data
Planet Zero has a mass of 4.0*10^23 kg and a radius of 2.0*10^6 m . With what kinetic energy should a 10-kg space probe be launched vertically from the surface of Zero so as to achieve a maximum distance of 4.0*10^6 m from Zero's center?

3. The attempt at a solution
I found the initial potential Energy, U=(GMm/radius planet Zero) and then the mecahnical energy at the end, E= - (GMm/2d)

its not right..HELP!!!

2. Apr 22, 2007

### mezarashi

I think most likely you are not using the right values for the distance.

The question is effective asking for the difference in gravitational potential of two configurations, and they are:

1. The space probe on the surface of this planet (distance of 2.0x10^6 from center)
2. The space probe at a distance off the surface (distance of 4.0x10^6 from the center)

Try doing the calculations carefully again.

3. Apr 22, 2007

### hage567

How do you know it isn't right? What did you get for your final value? Be careful of your signs.