# Homework Help: 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."

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook