Two identical metal spheres having charges +q and +q respectively. When they are separated by distance r, exerts force of repulsion F on each other. The spheres are allowed to touch and then moved back to same separation. The new force of repulsion will be

Two spheres carrying charges +6muC and +9muC , separated by a distance d, experiences a force of repulsion F. When a charge of -3muC is given to both the spheres and kept at the same distance as before, the new force of repulsion is

Two identical metals balls with charges +2Q and -Q are separated by some distance and exert a force F on each other . They are joined by a conducting wire , which is then removed. The force between them will now be

Two identical balls having like charges and placed at a certain distance apart repel each other with a certain force. They are brought in contact and then moved apart to a distance equal to half their initial separation. The force of repulsion between them increases 4.5 times in comparision with the initial value. The ratio of the initial charges of the balls is

Two identical spheres each of mass M and radius R are separated by a distance 3R. The force of attraction between them is proportional to