- #1

redivider

- 8

- 2

## Homework Statement

Calculate the gravitational force between a point mass and a circular platform.

## Homework Equations

G=m1*m2/r^2

## The Attempt at a Solution

http://i.imgur.com/dfZf9GK.jpg

The actual solution is different. They integrated by the angle between a/r (alpha) but i do not understand the cos(alpha) at the start, check this out:

http://i.imgur.com/nwxhCEb.jpg

Can anyone explain this please? Thanks.