A uniform rod of mass M and length 2a lies along the interval [-a, a] of the x-axis and a particle of mass m is situated at the point x = x . Find the gravitational force exerted by the rod on the particle.
Two uniform rods, each of mass M and length 2a, lie along the intervals [-a, a] and [b - a, b + a] of the x-axis, so that their centres are a distance b apart (b > 2a). Find the gravitational forces that the rods exert upon each other.