# Altitude of Geostationary Orbit

duchuy
Homework Statement:
Deduce at what distance from the center of the Earth are positioned the geostationary satellites which, observed from the terrestrial frame of reference, are motionless in the sky.
Relevant Equations:
T = 2piR / v
Hi,
They gave me this formula T = 2piR / v, with T the revolution period of the satellite, R the distance between the center of masses and v the velocity.
They gave me the value of G and the eath's mass and asked to determine the value of R.
I don't even see fromwhere I should start...

Gordianus
Have you studied what Mr. Newton said about gravitation?

• berkeman
duchuy
Have you studied what Mr. Newton said about gravitation?
Probably I have, but I'm not quite sure how I would use those formulas for an object in geostationary orbit... and I'm taking physics as a minor so I don't really remember much

Gordianus
O.K. Can you make a search about Newton's gravitation law and circular movement?

Gold Member
And, do you know what a 'geostationary' orbit is.

rsk
If a satellite appears to be stationary above the earth, what must its period T be? Can you also write an expression for v in terms of T and R? Then you'd be left with an expression with R as the only unknown.

BUT

Usually to tackle a Q like this, rather than using that equation you've quoted, I'd start from the fact that the gravitational force on the satellite is what provides the centripetal force. So if you can write an expression for each of these (I usually prefer the mrω² version for centripetal force), and equate them, you can do it from there - though you still need to know T of course.
In the end, it will get you to the same place, but doing it this way helps you to understand and therefore remember how this works.

• Keith_McClary