1. The gravitational force field created by the mass M and acting on the mass m is r F = -GMm- r31 where r(x, y, z) = (x, y, z). = 1. In the following calculations, assume you are using units where GMm Find the flux of F through a horizontal plane z = a. Surprisingly, the answer is inde- pendent of a. Hint: parameterize the plane in terms of u and v and then evaluate the flux integral by using polar coordinates in the uv plane.