The gravitational force on a point mass m due to a point mass m at the origin is a gradient field with potential u(r)= (gmm)/r , where g is the gravitational constant and r = (x^2 + y^2 + x^2)^(1/2) is the distance between the masses a. find the components of the gravitational force in the x-, y-, and z-directions, where f(x, y,z) = -gradientu(x, y,z) b. show that the gravitational force points in the radial direction (outward from point mass m) and the radial component is f(r) = (gmm)/(r^2) c. show that the vector field is orthogonal to the equipotential surfaces at all points in the domain of u