# Star system

1. Jan 15, 2012

### zezima1

I recently did an exercise where I had to calculate the total energy needed to separate the stars completely from each other - i.e. make the distance between them infinity.
One then had to calculate the potential energy between them as well as their kinetic energies. But theres something I don't get here - why do you have to use the kinetic energy in the calculations too. Couldnt you imagine a situation where the kinetic energy was the same after they had been separated by a distance of infinity.

2. Jan 15, 2012

### Simon Bridge

Work needed to separate the stars to infinity is the potential energy of the system in it's initial state. The total energy of the system is the potential energy and the kinetic energy.

Check the wording of the problem.

3. Jan 15, 2012

### aaaa202

Well the assignment explicitly asks: What amount of energy is needed to separate the stars to a distance infinitely far from each other.

4. Jan 15, 2012

### Simon Bridge

Well then, I'd say you have a point :)