a square of edge length 15.0 cm is formed by four spheres of masses m1 = 8.00 g, m2 = 3.50 g, m3 = 1.50 g, and m4 = 8.00 g. In unit-vector notation, what is the net gravitational force from them on a central sphere with mass m5 = 2.20 g?

Answer 1

To simplify this, look at diagonols. The net force on the center from two opposite corners is G(2.2)/d^2 (M1-Mopposite)

do that twice, for opposite corners. then do the vector addition of two vectors at 90 degrees, the result is easy to compute using pyth theorm.