1. Oct 7, 2007

### aligass2004

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

The asteroid belt circles the sun between the orbits of Mars and Jupiter. One asteroid has a period of 4.2 earth years. What are the asteroid's orbital radius and speed?

2. Relevant equations

T = 2pi sqrt(r/g)

3. The attempt at a solution

I tried manipulating the above equation to solve for r. I got 4.383, but it was wrong.

2. Oct 8, 2007

### Astronuc

Staff Emeritus
3. Oct 8, 2007

### aligass2004

I used 9.81 for the value of g.

4. Oct 8, 2007

### D H

Staff Emeritus
Why did you do that? You need to use the universal gravitational constant G, not the Earth's standard gravitational acceleration, g. Moreover, this equation,

$$T = 2\pi \sqrt{\frac r g}$$

is not quite. What are Kepler's laws?

5. Oct 8, 2007

### aligass2004

I have no idea. We didn't discuss them in depth.

6. Oct 8, 2007

### D H

Staff Emeritus
You were trying to use one of Kepler's laws here,

$$T = 2\pi \sqrt{\frac r g}$$

but you did it wrong. Where did you get that equation from? Look over your text and your notes.