Consider two identical solid metal spheres each of mass 2kg.
(i) The spheres are kept with their centres 50cm apart. A second arrangement keeps the same spheres 25cm apart. Without performing any numerical calculation, explain how the gravitational force in the second arrangement compares with that in the first arrangement.
(ii) In a third arrangement, the original 50cm separation is used, but one sphere is replaced by another of mass 4kg. Explain qualitatively, without calculation, how the new force compares with that in the first arrangement.
(iii) Give the reason for your answers in parts (i) and (ii) on the basis of the law of gravitation.