How to calculate displacement

What is relative velocity? in which condition is relative velocity known by adding the velocity of the first body and that of the second body

The diagram shows four locations in the electric field of a positive point charge m. at which location is the electric potential the greatest.

Four point charges each having charge q are located at the corners of a square having sides of length a. find symbolic expressions for the following. (a) the total electric potential at the center of the square due to the four charges (use any variable or symbol stated above along with the following as necessary: ke.) vtotal= (b) the work required to bring a fifth charge p from infinity to the center of the square (use any variable or symbol stated above along with the following as necessary: w=