Four indentical masses m are kept at the corners of a square of side a. Find the gravitational force exerted on one of the masses by the other masses.

Four particles each of mass m are kept at the four vertices of a square of side 'a' . Find gravitational potential energy of this system.

Four particles each of mass m are kept at the four vertices of a square of side 'a' . Find graitational potential energy of this system.

Four particles of masses m, 2m, 3m and 4m are placed at the four corners of a square of side a. Find the gravitational force on a particle of mass m placed at the centre of the square.