# Homework Help: Refreshing kepler problems.

1. Apr 28, 2006

### fargoth

im a private teacher now for first year students... and today my student asked me a question i didnt know the answer to... so i said i'll look it up, but im going out with friends :tongue2:

so if you could help and save me the time id really appreciate it.

the problem is finding the maximum radius of an eliptic route.
we know the tangential speed of the body at the point of the minimal radius.
so according to the advertised solution for the problem, the equation should be:
$$\frac{mv_{max}^2}{2}-\frac{A}{R_{min}}=\frac{(mv_{max}R_{min})^2}{2mR_{max}^2}-\frac{A}{R_{max}}$$
but we couldn't understand why it was $$E_k+U=U_{eff}$$ and not $$E_k+U_{eff}(R_{min})=U_{eff}(R_{max})$$

Last edited: Apr 28, 2006
2. Apr 28, 2006

### fargoth

nm, found my answer... while thinking at the pub