# Potential energy of a rocket

1. Mar 20, 2009

### pkc111

Can someone please explain to me whether the potential energy of a rocket increases as it accelerates and moves further from earth ?

My immediate answer is yes, but if W=dKE, then all of the work is being converted into KE and not PE ??

Thanks very much

2. Mar 20, 2009

### tiny-tim

Hi pkc111

there are two forces on the rocket … the engines, and gravity.

work done by gravity (or any other conservative force) is just another name for PE

3. Mar 20, 2009

### pkc111

Thanks Tiny Tim

4. Mar 20, 2009

### pkc111

So if there are 2 forces acting on the rocket, how does W=dKE?

5. Mar 21, 2009

### Staff: Mentor

It doesn't. W=dKE+dPE

6. Mar 21, 2009

### Staff: Mentor

If you include the work done by all forces on the rocket including gravity, then W = ΔKE. But since gravity is a conservative force we usually represent its effects by introducing a gravitational PE. In that case, if we just consider the work done by non-conservative forces (the "engine force" only, not gravity, which is already included in PE), then W = ΔKE + ΔPE.

7. Mar 21, 2009

### pkc111

So

W(Net) = Sum(Fs)= dKE

right?

8. Mar 21, 2009

### Staff: Mentor

Yes, if you include gravity as a force acting on the rocket. (No PE term.)

9. Mar 21, 2009

### pkc111

woohoo!
thank you all very much