Simple point charge location problem

[kirby2]

Point P in the figure is equidistant from two point charges +Q/-Q of equal magnitude. If a negative point charge is placed at P without moving the original charges, the net electrical force the charges +Q/-Q will exert on it is?

figure: http://goo.gl/EAADC

ATTEMPT: i think P will move directly upward because the -Q charge will repel it in the x-axis and the +Q will attract it in the x so there is no x movement. However, since these forces are in linear, both of them do have an upward components as well. This is why i think the answer is "directly upward." Is this right?

 

[Doc Al]

Yes, you are correct. But think in terms of forces, not 'movement'.