Consider this system of charges in the picture, where 2 charges +Q and 2 charges -Q are located, alternated, in the vertices of a square (a is the side).

a) Suppose that one of the -Q charges gets "kicked" and is threw out with a velocity v0, while the other three charges are in a state of rest. If the moving charge has a mass m, what's its velocity at an infinite distance from the other charges (result in the figure)?

b) Suppose that the other -Q charge has a mass m too and is moved away with a velocity v0. When it's at an infinite distance from the +Q charges, its speed is bigger, lesser or equal to the one found in the point a)? Explain.