# Circular Motion Problem.

1. Sep 29, 2004

### pulau_tiga

Hi!

I'm working on a circular motion problem, and I'm not sure on how to go about doing it.

The question:
A spacecraft moves in a circular orbit with a speed of 7360 m/s with a period of 6270. seconds. The radius of the spacecraft's orbit is 7.34 x 10^6 m and the radial acceleration of the satellite is 7.38 m/s^2. In order to begin its re-entry, the spacecraft engines are fired to provide an acceleration of 6.60 m/s^2 in a direction opposite to its velocity. What is the magnitude of the spacecraft's total acceleration just after the engines begin to fire?

My first try at the question involved simply adding a negative 6.60 m/s^2 to the radial acceleration (7.38 m/s^2). I came up with 0.780 m/s^2 for the spacecraft's total acceleration which is wrong.

If anyone could point be in the right direction on how to go about this problem it would be greatly appreciated.
Thanks.

2. Sep 29, 2004

### Staff: Mentor

The two accelerations you are trying to add are vectors. They are perpendicular to each other. (One is radial, the other tangential.) Add them as vectors.