# Homework Help: Universal gravitation + orbits question

1. Jun 7, 2009

### davie08

1. The problem statement, all variables and given/known data
A 450kg satellite is to be placed at an altitude of 2.45 x 10^6m above the earth surface. Calculate the period the satellite will have when orbiting at that altitude.

2. Relevant equations

m2g = Gm1m2/R^2 = m2v^2 = m2(4pie)^2 R /T^2 = m2 2pie v/T

Ac=4pie ^2 R / T^2

3. The attempt at a solution

Alt= r- rp
2.45x10^6m= r -6.37x10^6m
8.82x10^6m = r

I dont no what equation to use next

2. Jun 7, 2009

### Cyosis

This is wrong it should be $Gm_1m_2/R^2 = m_2v^2/r$

Is also wrong I am not sure what you did here. You're also making one big equality chain which does not hold.

Start with $Gm_1m_2/r^2 = m_2v^2/r$. Do you know a formula that relates v to T for a circular orbit?

3. Jun 7, 2009

### Stratosphere

there are several aproches to this problem. If it is a circuler or bit you could use use
$$v_{orbit}=\sqrt{r_{orbit}g_{orbit}}$$

If it is not a circuler orbit you could use,

$$T^{2}=\frac{4\pi^{2}\mu}{Gm_{1}m_{2}}r^{3}$$