# Homework Help: Net grav force

1. Oct 13, 2007

### bigtymer8700

1. The problem statement, all variables and given/known data
Each ball weighs 3.00 kg A is 10cm from C to the left and B is 40cm to the right of A

2. Relevant equations

F=Gm1m2/r^2

3. The attempt at a solution

ive tried adding the forces that each ball apply to A and subtracting it. i know each has its own force acting on A but dont know how to figure it out with 3 objects

2. Oct 14, 2007

### Kurdt

Staff Emeritus
Force is a vector. You have two force acting in opposite directions on ball A. How would you work out the net force then?

3. Oct 14, 2007

### bigtymer8700

Well you already know that each force is acting in the x direction and with gravity the farther away the less the gravitational force so wouldnt you just have to subtract the sum of each force?

4. Oct 14, 2007

### bigtymer8700

F=6.67e-11 (3kg) (3kg))/.04^2 i calculated that for the force of B on A and i got 3.75e-7N

for force of C on A i got 6.003e-7N. Now each of these balls is exerting its own force on A but one is stronger than the other because of the distance so isnt the net force just calculated by the difference?

5. Oct 14, 2007

### Kurdt

Staff Emeritus
If you have to calculate the net force on A then both balls B and C are to the right of it and the forces will add. I was a bit unsure which ball you were wanting to calculate the net force on. The description of the system was a bit ambiguous as well.

6. Oct 14, 2007

### bigtymer8700

In the picture given to me Ball C is to the left of A and ball B is to the right they are on different sides sorry if the description was hazy.