Satellite 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