# What is the altitude above earth's surface?

#### oosta

Here's the question. I'm not sure how to apporoach it.

A satellite has an orbital speed of 4.2 x 10 exponent 3 m/s. What is the altitude above earth's surface? (M of earth = 5.98 x 10 exponent 24 kg, radius of earth = 6.38 x 10 exponent 6 m)

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#### berkeman

Mentor
Thread moved to Homework Help.

What equations do you think apply? What do you know so far about forces in circular motion? What is the general equation for the gravitational attraction of two masses?

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#### oosta

ok well, i think i should use the equation Fg = Gmm over r^2

but i dont know how to find the other mass. and the radius of the satellite.

#### berkeman

Mentor
ok well, i think i should use the equation Fg = Gmm over r^2

but i dont know how to find the other mass. and the radius of the satellite.
That's one of the two equations you need. What is the equation for uniform circular motion that relates the velocity (angular or orbital linear) to the mass, radius and central force?

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