# Universal Gravitation - Satellites

1. Dec 13, 2004

### BbyBlue24

The Explorer VIII satellite, placed into orbit November 3, 1960, to investigate the ionosphere, had the following orbit parameters: perigee, 459 km; apogee, 2289 km (both distances above the Earth's surface); period, 112.7 min. Find the ratio vp/va of the speed at perigee to that at apogee.

2. Dec 13, 2004

### enigma

Staff Emeritus
Welcome to Physicsforums, BbyBlue.

First off, questions like this should be submitted to the homework help section.

Second, before you can expect an answer, you should at least post what you have tried to get an answer.

It doesn't benefit you to have someone do your homework for you.

3. Dec 13, 2004

### BbyBlue24

FYI: This isn't a homework problem, I am doing random problems throughout the book to prepare for an exam tomorrow.

I have played around with equations of conservation of angular momentum and equations such as v=(2πr)/T and v=√(GMe/r)=√(GMe/Re+h). I tried using Vp=(Ra/Rp)Va, but I have gotten nowhere. Thanks!

4. Dec 13, 2004

### Pyrrhus

Well, by using conservation of angular momentum for the satellite

$$r_{perigee} v_{perigee} = r_{apogee} v_{apogee}$$

we rearrange this to:

$$\frac{v_{perigee}}{v_{apogee}} = \frac{r_{apogee}}{r_{perigee}}$$

you don't need the period.

5. Dec 13, 2004

### BbyBlue24

I have; Vp/Va = Ra/Rp = 2289/459 = 4.99 km

6. Dec 13, 2004

### Pyrrhus

The problem states distances above the surface, you need to add the Earth radius to each of those radius.

7. Dec 13, 2004

### BbyBlue24

I got it, thanks!!! I think that's all I have tonight, thank you very much!

8. Dec 13, 2004