# Homework Help: Protostar - Thermal energy change

1. May 11, 2010

### Fleet

1. The problem statement, all variables and given/known data

I have to calculate the change in a protostar's thermal energy $$\Delta E_{term}$$ on a year.
I am given the protostar's luminosity $$L=3,5\cdot 10^{28}\,W$$
Furthermore I am told that the energy that the star radiates comes from the lost potential energy under the star's contraction.

2. Relevant equations
The virial Theorem: $$E_{total}=E_{kin}+E_{pot}=\frac{1}{2}E_{pot}=-E_{kin}$$

3. The attempt at a solution
I can calculate the "radiated" (lost) energy: $$3,5\cdot 10^{28} W\cdot 365,25\cdot 24\cdot 60^2 \frac{s}{y}=1,105\cdot 10^{36} J$$
But I don't know how if this is right or how to get to it by arguing from the virial theorem.

I really hope you can help me.

Best regards.