# Homework Help: Satellite motion

1. Nov 24, 2005

### SS2006

A satellite orbits the earth at a height of 200 KM in a cirlce of radius 6570 km. Find the speed of the satellite and the time taken tocomplete one revolution. Assume teh earth's mass is 6.0 X 10 exp 24.
(Hint: The gravitation force provides the centripetal force)

i found Velocity using:
v = square root of gravity constant * m central / r

but they want the time, what can i use
thanks

2. Nov 24, 2005

### rocketboy

try using d = vt
therefore, t = d/v

you found the velocity, and you have the radius of its circular path.

3. Nov 24, 2005

### SS2006

so 6570/7.8
gives 842 seconds i assume? dividign b 60 just gives 14

4. Nov 24, 2005

### mezarashi

The d mentioned by rocketboy is the circumference of the orbit, not the radius of orbit.

5. Nov 24, 2005

### rocketboy

yea, sorry for not making that more clear. The 'd' I mentioned above is the total distance covered by the satellite. So if you have the radius of its circular path, then you need to find the circumference of this circle. This circumference is the distance that the satellite has travelled.

Once you have this distance, you can find the time taken using the equation I mentioned above, which you should know from your basic kinematics lessons.

6. Nov 24, 2005

### cscott

Alternatively you could use $$G\frac{m_E}{r^2} = \frac{4\pi^2r}{T}$$