# Physics satellite velocity and period

1. Sep 30, 2013

### astru025

1. The problem statement, all variables and given/known data

a. What is the tangential velocity of a satellite in a circular orbit 300km above the surface of the Earth?

2. Relevant equations
Velocity of a satellite= v^2= G (Me/r)

3. The attempt at a solution
V^2= 6.67E-11 (5.98E24/6.37E6)
I calculated this and my answer proved incorrect. How do I incorporate the "300 km above earths surface" into this equation?.

2. Sep 30, 2013

### Staff: Mentor

Use that to calculate the radius of the orbit, which will be "r".

3. Sep 30, 2013

### astru025

I use 300km to calculate the radius of the orbit. What is the equation for the radius?

4. Sep 30, 2013

### Staff: Mentor

In your calculation, you set r = radius of the earth. But that's not correct; r should be the radius of the orbit, which is bigger than the radius of the earth (by the given amount).

First calculate the radius of the orbit, then use it in your formula to find the speed.

5. Sep 30, 2013

### astru025

Okay thank you. Is there a special equation to find the radius of the orbit?

6. Sep 30, 2013

### Staff: Mentor

Just add the altitude of the orbit, which was given, to the radius of the earth.

7. Sep 30, 2013

### astru025

Okay so now I have : v^2= G (6.67E-11) x ((Me (5.98E24) / (r + 300 km. (6670 km))
Is this correct? So I got 244540.39.

8. Sep 30, 2013

### astru025

That answer was incorrect. What am I doing wrong?

9. Sep 30, 2013

### SteamKing

Staff Emeritus

10. Sep 30, 2013

### Staff: Mentor

I don't understand how you got that answer. Did you make sure to put the radius in meters, not km?

11. Sep 30, 2013

### nasu

This must be it. You are off by a factor of about √1000. The radius should be in meters.

12. Sep 30, 2013

### astru025

Okay I finally came up with 1768897.96 m/s

13. Sep 30, 2013

### astru025

Okay now I came up with 7733.046. This must be correct. Miscalculation in my previous try.

14. Sep 30, 2013

### astru025

This proved correct! Thanks so much. Always need to check my units :)