# Work required to take object from planet to infinity

1. Apr 19, 2015

### JesseJC

1. The problem statement, all variables and given/known data
A terrestrial creature with mass m = 100kg to is standing on a planet the same size as our moon

1.) what is the gravitational acceleration on the surface of this planet ? Ag = GM/R^2 = 1.63 m/s

2.) work required to take creature off of planets surface and into space ?
2. Relevant equations
R = 1.74x10^6
M = 7.36x10^22
m = 100kg

3. The attempt at a solution

2. Apr 19, 2015

### Noctisdark

It's not to infinity, it's enough to take him away where the gravitationnal field won't do so much, and i think (maybe) W = F.s will
F is just equal to gravitationnal force on the creature,

3. Apr 19, 2015

### grzz

But one has to take into consideration that as the distance s is increasing, the force F is decreasing.

4. Apr 19, 2015

### JesseJC

Alright, so I'm thinking that I'll need to multiply the gravitational force by a certain distance and that's it, I'm not working with integrals or anything in this course, but the question asks for me to calculate work needed to send the object to infinity, which is pretty ambiguous. It also says that it just needs to be out of the gravitational pull, like you said ^^^. I don't understand what distance I can apply.

5. Apr 19, 2015

### grzz

If integration is not to be used, then one can use the idea of 'gravitational potential'.

6. Apr 19, 2015

### AlephNumbers

Oh, but it is. Jesse, you need an equation to represent the gravitational potential energy of the creature at the surface of the planet. That shouldn't be too difficult to find if you don't know it off the top of your head.