Distance from Satellite to Earth Question

[Sevenheartz]

Homework Statement

A satellite in a circular orbit around Earth has a speed of 7.15x10³ m/s. Determine, in terms of Earth's radius (radius of earth= 6.38 x10⁶m):

a) the distance the satellite is from Earth's centre
b) the altitiude of the satellite

Homework Equations

F_G = GMm / r²
F_c = mv² / r
G = 6.67 x 10^-11

The Attempt at a Solution

I'm seriously unsure on how to even start on this one, because I'm not sure what they mean by 'in terms of Earth's radius.' The answer key says 1.22 r_earth for a. Do you have to do this through proportionality and ratios?

In terms of writing down the given/known:
v = 7.15 x 10³ m/s
r_earth = 6.38 x 10⁶ m
M_earth = 5.98 x 10²⁴ kg
G = 6.67 x 10^-11 Nm²/kg²

I can't figure out the force of gravity because I don't have the mass of the satellite, so that cancels out finding F_c as well since I need the mass for that too.

Any help on how to start this would be appreciated, thank you.

 

[LowlyPion]

You won't need the mass of the satellite.

F_c = mv²/r = F_g = GMm/r²

v² = GM/r

 

[Sevenheartz]

You won't need the mass of the satellite.

F_c = mv²/r = F_g = GMm/r²

v² = GM/r

Oh, I see. But I'm still confused by "in terms of Earth's radius," what exactly do they mean by that?
By the way, I used v² = GM /r to find that r = 5.58 x 10¹⁰ Would that be the radius from the Earth's centre to the satellite?
Thanks for your help

 

[Kurdt]

In terms of Earth's radius means how many multiples of the Earth's radius is the satellite orbiting at.

 

[Sevenheartz]

In terms of Earth's radius means how many multiples of the Earth's radius is the satellite orbiting at.

Ah, I got it now. Thanks for the help Kurdt and LowlyPion.