# Homework Help: Compute the speeds of the star

1. Sep 27, 2010

### leonne

1. The problem statement, all variables and given/known data
Compute the speeds (in km s^-1) of S0-2 and S0-16 at pericenter and apocenter.
star S0-2: period P = 15:8 yr, semimajor axis a = 1025 AU, and
eccentricity e = 0:880;

2. Relevant equations
Vp=((1+e)u)/(1-e)a))^1/2 va=((1-e)u)/(1+e)a))^1/2

u=(m1m2)/m1+m2
3. The attempt at a solution
I found this formula to calc the velocity of the 2 but I was never given a mass for the star. This is a 3 part problem and the other two asked to find mass of black hole and then Compute the pericenter and apocenter distances of the star. Do i use a diffrent formula? or I have to find the mass of the star? Thinking maybe to find mass of the star to use P^2=(4pie^2 a^3)/G(m1+m2) m1 ill make it the mass of the black hole and solve for m2, is that right?

Note the problem asks to do this for two stars idk if this changes anything in the formula but both stars orbit the black hole.
thxs