An air bubble with a radius 4 an iron ball of same radius are present in water. The distance between the centers of bubble and iron ball is 1 m. Neglect the mass of air in the bubble. The mass of water drop whose size is equal to the size of bubble is 1.5 kg . The densities of water and iron are 1 gm/cm3 and 8 gm/cm3 respectively. The force between bubble and iron ball is .... (approximately)