3.4x10^-8 N of force directly towards the sphere in the opposite corner of the square.
The gravitational attraction of two masses towards each other is
F = G(m1m2/r^2)
where
G = gravitational constant
m1,m2 = masses
r = distance between the centers of the masses.
So the force being exerted by the masses alone an edge of the square would be
F = 6.674x10^-11 N(m/kg)^2 * ((8.5 kg)^2)/((0.52m)^2)
F = 6.674x10^-11 N(m/kg)^2 * (72.25 kg^2)/(0.2704 m^2)
F = 6.674x10^-11 N(m/kg)^2 * 267.1967 (kg/m)^2
F = 1.78327x10^-8 N
There are 2 masses that affect a mass on a corner so that the sum of their vectors will result in a 3rd vector aiming towards the mass in the diagonal corner. So
sqrt(2(1.78327x10^-8 N)^2) = 2.52193x10^-8 N
The mass in the diagonal corner will also be attracting. The distance to that mass is sqrt(2*(0.52m)^2) = 0.735391052 m
F = 6.674x10^-11 N(m/kg)^2 * ((8.5 kg)^2)/(2*(0.52m)^2)
F = 6.674x10^-11 N(m/kg)^2 * (72.25 kg^2)/(0.5408 m^2)
F = 6.674x10^-11 N(m/kg)^2 * 133.5984 (kg/m)^2
F = 8.916355x10^-9 N
This vector will be along the same line as the combined vector from the other 2 masses, so they'll add directly.
F = 8.916355x10^-9 N + 2.52193x10^-8 N = 3.4136x10^-8 N
Since we have 2 significant figures in our data, the result rounded to 2 significant figures is 3.4x10^-8 N
