# Gravitations! need help with formula

1. Mar 15, 2010

### Sirsh

-Deleted-

Last edited: Mar 15, 2010
2. Mar 15, 2010

### rl.bhat

But when i substitute the values into the equation they dont both equal the same amount on each sides. help me please!
That has to be. What is your problem? Post a specific problem where you want to apply this relationship. Mainly this relation is used to compare the distances of two planets when their periods of revolution is known.

3. Mar 15, 2010

### Sirsh

2. Using your knowledge of circular motion and gravitation, derive an equation that shows the relationship between the orbital period (T) of a planet in a circular orbit and the radius of the planetary orbit (R).

4pi^2/GM = T^2/r^3

39.478/ 3.247E+14 = 1.08E+11/ 7.474E+21

1.215E-13 = 1.445E-11

I'm thought that the formula i had rearranged would have answered this question, except shouldnt both sides of the equations equal the same value when their values are substituted into the equation?

4. Mar 15, 2010

### Sirsh

-Deleted-

Last edited: Mar 15, 2010