# Gravitational Field Related Question

1. Aug 21, 2009

### wilson_chem90

A satellite is designed to orbit Earth at an altitude above its surface that will place it in a gravitational field with a strength of 4.5 N/kg.

a) Calculate the distance above the surface of Earth at which the satellite must orbit.

b) Assusming the orbit is circular, calculate the acceleration of the satellite and its direction.

c) At what speed must the satellite travel in order to maintain this orbit.

(I already found the answer for a) i got approximately 3034716.6 m above Earth)

For c) I know I can use the equation v = {GmE/r} ( {} = square root)

but i am not sure how to find the acceleration for b). the only thing i can think of is using
ac = v^2/r.

Any suggestions?

Thanks

2. Relevant equations

3. The attempt at a solution

2. Aug 21, 2009

### kuruman

Yes, it is the centripetal acceleration.

3. Aug 21, 2009

### wilson_chem90

but i would have to find the velocity first? in order to find the acceleration, right?

4. Aug 21, 2009

### kuruman

Yes, and you know already the expression for the velocity, speed more correctly.

5. Aug 21, 2009

### wilson_chem90

alright thank you very much, much appreciated

6. Aug 21, 2009

### ideasrule

This question can be done in a less roundabout way by writing out Newton's second law for the satellite:

F_net=ma
GMm/r2=ma
a=GM/r2

You'll realize that this is also the gravitational field strength, so acceleration = 4.5 N/kg = 4.5 m/s2. Remember that: gravitational field strength is equal to acceleration due to gravity.