# Star Equations & Derivations

1. Jan 18, 2008

### tony_cruz

Right I've got an exam at half past 4, tomorrow on a Saturday! I've spent the past few days doing past exam questions and a lot of them I'm able to do or at least work out for myself after a bit of time. Here's a couple I'm really stuck on so some help would be really really appreciated.

1. The problem statement, all variables and given/known data
*all = signs are proportional not equal. I thought it'd be easier than sticking k's everywhere.

Combine equations [1] and [2] to show to a good approximation that T = R^2
Assume that all these stars have the same average density.

2. Relevant equations
[1] L = M^3.3
[2] L = R^2*T^4

3. The attempt at a solution
Don't really know where to start with this one. I've tried re-arranging all of the equations and substituting in, but I always get stuck very early on. Mathmatical derivations really aren't my strong point.

On a similar vain, I have this equation.

Show that L = T^B and derive the value of B
(I know B is ~-0.7 btw, I just don't know how to derive that)
again = is actually proportional

2. Jan 18, 2008

### malawi_glenn

How is the mass related to volume and volume to radius?

and use "Assume that all these stars have the same average density."