# Homework Help: Shuttle moving in a circular orbit

1. Mar 10, 2013

### clownbaby

The space shuttle is moving in a circular orbit with a speed of 7.8km/s and a period of 87min. In order to return Earth, the shuttle fires its retro engines opposite to its direction of motion. The engine provide a deceleration of 6m/s^2 that is constant in magnitude and direction. What is the total acceleration of the shuttle?

can't seem to understand how to start solving it. don't i need the radius of orbit?

2. Mar 10, 2013

### lep11

Yes. Use the universal law of gravitation to solve radius of the orbit.

3. Mar 10, 2013

### clownbaby

i tried to solve it but im not sure if it is correct.

ω=2pi/T
360/87x60=2/29
V=ω.r
2/29xr=7800
r=113100m = 113,1km
a = v^2/r = ω^2r (circular motion equations)
(2/29)^2x113,1=78/145 km/sec^2 = 15600/29 m/sec^2

the retro engine deceleration is 6m/sec^2
15600/29-6=15426/29 m/sec^2

is it correct? i really need help, confirmation on this.

4. Mar 10, 2013

### clownbaby

gravitation law requires masses if am not mistaken and also i think this is a circular motion question.

5. Mar 10, 2013

### lep11

Satellite mass will cancel out.