1)According to Archimedes principle, a body when immersed in a fluid shows an apparent loss of weight which is equal to the weight of the fluid displaced by the body. So aheavy stonewhen underwater, is acted upon by upthrust due towater, which ultimately reduces the true weight of thestone.

1. According to Archimedes principle, a body when immersed in a fluid shows an apparent loss of weight which is equal to the weight of the fluid displaced by the body. So a heavy stone when under water, is acted upon by upthrust due to water , which ultimately reduces the true weight of the stone.

2.smaller the area - larger the pressure on the surfaceto make sure the foundation of the tall buildings and dams are strong, they are built with a broader basement .so, if the area in the bottom is higher then the pressure exerted by the buildings and dams on the ground would automatically be less .

2) Buildingsare massive structures which exerts tremendous pressure on the ground and likely to sink. To avoid sinking theirfoundationsare madewide, so that pressure on the ground decreases.