# Homework Help: Gravitational force and constants

1. Apr 20, 2010

### juggalomike

1. The problem statement, all variables and given/known data
Three identical masses of 570 kg each are placed on the x axis. One mass is at x_1 = -10.0 cm, one is at the origin, and one is at x_2 = 43.0 cm.

What is the magnitude of the net gravitational force F_grav on the mass at the origin due to the other two masses?

Take the gravitational constant to be G = 6.67×10−11 N * m^2/kg^2.

2. Relevant equations

F=G(m1m2/R^2)

F=F1-F2

3. The attempt at a solution

-(6.67*10^-11)*(570^2)/(-.1)^2 - (6.67*10^-11)*(570^2)/(.43)^2 =-0023 N

What am i doing wrong?

2. Apr 20, 2010

### thebigstar25

maybe you want to reconsider the direction of each force .. (you should do vector subtraction) ..

3. Apr 20, 2010

### juggalomike

tried it, still telling me the answer is not 0...

4. Apr 20, 2010

### thebigstar25

why should the answer be zero?

5. Apr 20, 2010

### juggalomike

The answer is not zero, however because my number is so small it is considering it to be 0

6. Apr 20, 2010

### Dick

The answer is small. But in the expression you gave you are adding both forces in the negative direction. The sign should be different between them. One should be pulling in the positive direction and the other in the negative. I think this was thebigstar25's point.

7. Apr 21, 2010

### thebigstar25

thanks Dick for explaning my point in a better way .. I think now juggalomike can solve the problem ..