# Homework Help: Relationship between momentum,KE and internal energy

1. Feb 26, 2006

hello

I just realised I'm having some trouble figuring out the relationship between conservation of momentum and kinetic energy and internal energy in isolated system.

We learned that total momentum gets conserved if two object collide in isolated system.

But when learning about energies they tell you that if collision is not elastic then part of kinetic energy will get transformed into internal energy. So if collision is elastic, then first object will give certain amount of its energy via work to second object

before

KE of O1= 10
KE of O2= 4
total KE = 14

and after collision

KE of O1 = 8
KE of O2 =6
total KE =14

But if collision is not elastic then KE transformed into internal energy is for example W(internal)=2

If that is the case then total KE available to objects O1 and O2 in isolated system is merely KE - W(internal)=12.

So how can momentum get conserved?

thank you

2. Feb 26, 2006

### Astronuc

Staff Emeritus