# Work done and P.E

1. Dec 8, 2003

### BillyCheung

Dear all

I know that E(grav) = -GmM / r, Can I use Work done = F x s to calculate the P.E between two mass of the space? Thank a lot.Good Bye

Billy

2. Dec 8, 2003

### KLscilevothma

No, I don't think so because F isn't a constant in a G-field, but we can use integration to derive the formula, E(grav) = -GmM / r.

dw = - F dx

$$\int ^{w'}_{0} dw = - \int ^{\infty}_{r} \frac{GMm}{x^2} dx$$

$$w' = -\frac{GMm}{r}$$

Where w' is the work required to take an object from infinity to a particular point in a G-field, with distant r away from the other object.