boat anchor lake

A fisherman rowing his boat on a very small lake throws his anchor into the water. Does the water level of the lake rise, fall, or stay the same?

Solution by Marty McHugh

While the anchor is in the boat, its weight displaces a volume of water V1 equal in weight to the anchor (by Archimedes' principle). After being thrown overboard, the sunken anchor displaces a lesser volume of water V2, equal in volume to the anchor. V2 is less than V1 because the anchor is denser than water (otherwise it would not sink!) So, with less water displaced, the level of the lake falls.