# Statellite quest

1. Nov 2, 2005

### UnD

Umm i am kind of lost,
calculate the work done to location a 150kg satellite into a geostationary orbit.

2. Nov 2, 2005

### Tide

HINT: It takes energy to lift an object to that height above the Earth and it takes energy to get it up to speed so it will orbit.

3. Nov 2, 2005

### UnD

1/2 mv^2 = mgh
i know that only
Umm I know the -Gm=m/r^2
but i don't think it applies to this kind of question.

Plz help

4. Nov 2, 2005

### HallsofIvy

Staff Emeritus
Unfortunately, you don't know that! That's saying "kinetic energy equals potential energy" which applies when you have an object losing kinetic energy (perhaps by rolling down hill) and converting it to kinetic energy (conservation of energy). That is not what happens here. You use the rocket fuel to give the satellite enough potential energy to reach the correct height and enough kinetic energy to reach the correct speed for an orbit at that height.
Unfortunately, you don't know that either. In fact, it makes no sense as the two sides have different units. You are probably half-remembering that gravitational force between two objects of masses M and m, distance r apart, is -GmM/r^2. If this is homework, don't you have your textbook in front of you?
If we take gravitational potential energy to be 0 at "infinity" (the standard) then the potential energy at distance r from the center of the earth is -GmM/r.
You need to do several things:
(1) Calculate or look up the distance, from the center of the earth at which a satellite would have a geosynchronous orbit. Use that to find the potential energy of the satellite.
(2) Calculate or look up the speed of that satellite. Use that to find the kinetic energy of the satellite.

The sum of those is the total energy that has to be given to the satellite.

5. Nov 2, 2005

### UnD

i don't have a textbook, haven't got a textbook from school, i will get one in couple of weekz;
COuld you please direct me to what formulas to use. THanks:shy: