I don't get what the conditions below exactly means.
Its which u they are talking about? Is the u the parent or children? Does it mean u = B? and the children are A,C,D?
if u is in the quadtree rooted by v:NW then u:x < v:x and u:y ≥ v:y;
1) Direction the are going to the north?
2) Sorry, its cos(30) I overlooked the value. Should I do the whole calculation of it?
Ok I have revise the forces and vectors addtion again and I will come back in few days!
I tried to solve this problem but somehow I don't get it really. What I have to do. What I also know in this context is if its the same charge it will not attract otherwise if its the opposite charge it will attract. How do I have to calculate each charge on the corner?