# Gravitational Field Strength Help

1. Oct 4, 2008

### shootingrubbe

Hello Everyone, I've been trying to get the answer to this problem for ages now and I just can't match my answer with the one in the back of the textbook. I hope you can let me know what I'm doing wrong.

1. The problem statement, all variables and given/known data
What is the gravitational field strength at a place 220 km above Earth's surface, the altitude of many piloted space flights.

2. Relevant equations
Fg = mg
Fg = Gm₁m₂/d²

3. The attempt at a solution
d = 6.60 x 10³ km
G = 6.67 x 10-¹¹ N.m²/kg²
m₂ = 5.98 x 10²⁴ kg
g = ? N/kg

Fg = mg = Gm₁m₂/d²
mg/m = Gm₁m₂/d²/m
g = Gm₂/d²
g = (6.67 x 10-¹¹ N.m²/kg²)(5.98 x 10²⁴ kg)/((6.60 x 10³ km)²)

And when I do this I always get the wrong answer when I compare it with the one in the back of the textbook. The answer in the back of the textbook is 9.1 N/kg [down].

Thanks.

2. Oct 4, 2008

### Rake-MC

Equation looks fine to me, I solved it and got 9.18 N/kg
what did you get?

3. Oct 4, 2008

### shootingrubbe

Thanks, I guess I was doing it right, I just forgot to convert the distance in to meters.

4. Oct 4, 2008

### Rake-MC

oh of course, how could I overlook that. I didn't follow your equation, I did it myself. I should have checked your equation more thoroughly!