# Satellite height from earth Question

1. Jan 17, 2005

### thomasrules

I hate this question:

I don't know if I'm doing something wrong because it seems so hard. Can i get someones way of doing this question...

Communications satellites are placed in orbit so that they remain stationary relatice to a specific area on the Earth's surface. They are given the name synchornous satellites because, to maintain such a position, their period as they orbit must be the same as the Earth's.
What is the height of such a satellite measured from
a) the centre of the Earth, and
b) the surface of the Earth

2. Jan 17, 2005

### vincentchan

If you hate it, then don't do it....

3. Jan 17, 2005

### dextercioby

They are called geostationary satellites.

Their trajectory can be a circle.Apply the 2nd law to the satellite in the inertial frame given by the center of the Earth.

Daniel.

4. Jan 17, 2005

### thomasrules

I'm not given an acceleration though

2nd law:?

net f=ma

ma=M(4pi^2r)/T^2

is that it?

5. Jan 17, 2005

### dextercioby

Okay,now use the fact that the movement is not in a straight line,but on a circle...

What is the RHS of your equation??

Daniel.

6. Jan 17, 2005

### thomasrules

man you've got to help me here......Okay I'll tell you what i've done...

i got (r+x) as my radius.....x being the distance from earth surface to satellite. therefore

4pi^2(r+x)/T^2=GM/(r+x)^2

7. Jan 17, 2005

### dextercioby

Perfect.Your equation is good.Now just plug in the numbers and tell me your result.Total distance (from the Earth's center).

Daniel.

8. Jan 17, 2005

### thomasrules

LOL that can't be right dext. I mean I get cubes when i cross multiply and it's all messed up......I get stuck later i can't find x

I got stuck at

x=7.51(10)^22/(1.2E14+1.9E7x+x^2)

THATS so wrong ain't it

9. Jan 17, 2005

### dextercioby

You needn't solve for "x".Your unknown is not necessarily "x".Think about it.

Daniel.

10. Jan 17, 2005

### thomasrules

dexter i need to know r+x which is equal to height but in order to know that I need to solve for x right......then add x with r which i have already......

I'm sorry but my iq is nothing compared to yours

11. Jan 17, 2005

### dextercioby

$$(R+x)^{3}=\frac{T_{rot}^{2}GM_{E}}{4\pi^{2}}$$

Daniel.

P.S.How about "thinking out of the box"???

12. Jan 17, 2005

### thomasrules

OMG !!!!! HAHAHAHAHAHA DEXTERCIOBY.....I'm so Amazed....seeing that equation was like magic to me.....like how the hell OMG
you know what I did was the following !!!!! :
4pi^2(r+x)(r^2+2rx+x^2)=Gmt^2

and then multiplied each one

THANK YOU OMNISCIENT ONE