# Missed class need some help again

1. Mar 27, 2009

### chewtoy929

how can I calculate the distance something is above the earth? as an example a 1750 kg satellite orbits the earth. it has a gravitational potential energy of 1.69*10^10 J. Its free fall accel is 6.44 m/s^2 how high is it.

How would I solve this? thanks.

2. Mar 27, 2009

### Staff: Mentor

Thread movdd to Homework Help forums.

Welcome to the PF, chewtoy. On homework and coursework questions, you must show us the relevant equations and also your initial attempt at a solution, before we can offer much in the way of tutorial help.

You appear to be studying uniform circular motion and gravitational forces. Show us the relevant equations from your textbook for this subject matter, and tell us your thoughts on how you might use those equations to approach this question.

3. Mar 28, 2009

### tnutty

Use this formula :

F_g = GMm/r^2

or

mg = GMm/r^2

4. Mar 28, 2009

### xcvxcvvc

dont you mean use a = GM/R^2? If a satellite is way above earth's surface, using little g(9.81) for any calculation would be wrong. the point of that equation is the gravitational pull ISN'T 9.81.

the force one mass pulls on the other mass is equal to gravitational constant 6.67...something * mass of object 1 * mass of object 2 divided by the distance from the centers of the objects squared:
GMm/r^2 = F

you know by now that f = ma

substitute for f, use your given a, and solve for r.