# Homework Help: Physics problems (gravitational acceleration and work)

1. Oct 30, 2005

### Leaping antalope

Need help with my physics homework.

1. Consider three masses that lie in the X,Y plane. The first mass, m1 lies at the origin, second mass, m2 lies at (0, Y2) and let the third mass, m3 lies at (X3, 0). Find an expression for the net gravitational acceleratoin at an arbitrary point in pace, (X,Y,Z) and show that if Z is much larger than Y2, X3, X, and Y that the acceleratoin varies approximately as Z^(-2).

2. How much work is required to dissemble the Earth. Assume that the planet is homogeneous with density p and radius R. Calculate te work required to remove shells of thickness dR from the planet and then integrate.

2. Oct 30, 2005

### big man

Do you maybe have any ideas on how to approach the questions at least??
It will increase the chances of getting a useful response to your problem.

3. Oct 30, 2005

### Leaping antalope

For this problem, I found out the three acceleration vectors to m1, m2, and m3. Then I added the three vectors together and got an expression for a net gravitational acceleration. But I don't konw how to do the last part of the question. When Z is much larger than Y2, X3, X, and Y, I tried to cancel the small variables but it didn't work.

For this problem, I know that dw=F (dot product) ds. In this problem, ds is the radius of earch. But I'm not sure what F is. Is it the gravitational force?