posted by Jenny .
Four 6.0 spheres are located at the corners of square of side 0.7m. calculate the magnitude and the direction of the total force exerted on one sphere by the other three.
Use symettry. The adjacent corners have two components of force each, but they are equal and opposite in one direction, so it reduces to just figureing the cosine 45 of one corner, doubling that component , then adding the force from across the square. Remember the across distance is s*(sqrt2)