# Force on satellite from earth

## Homework Statement

A communications satellite with a mass of 450 kg is in a circular orbit about the Earth. The radius of the orbit is 2.9×104 km as measured from the center of the Earth. A. Calculate the weight of the satellite on the surface of the Earth. B. Calculate the gravitational force exerted on the satellite by the Earth when it is in orbit.

## Homework Equations

Weight=mass*gravity

3. The attempt at a solaution
I found A. 4400 N
I dont know how to try to find B.

## Answers and Replies

ideasrule
Homework Helper
What's the formula for gravitational force?

for B) use newtons universal law of gravity.

namely:

$$F=\frac{GMm}{r^2}$$

G= newtons gravity constant
M= mass of earth
m= mass of satellite
r= radius of orbit

note:(both newtons constant & the mass of earth can be found on the internet)

What's the formula for gravitational force?

sorry ideasrule, i gave it away i tried that but it was wrong
F=((6.67E-11)(5.97E24)(450))/(2.9E4)^2=213067241.4 this isnt right, what am i doing wrong
G=6.67E-11
mass od earth= 5.97E24

you must convert your radius from Km to m. Always double check your units...

(it cost NASA millions one time)

alright, i got it, thanks