Shark attack

A ship is loaded with cubic sealed containers, each with a side length of 2 m and filled with merchandise of different specific gravities. The total weight of each container is indicated on a label. During a seastorm, it becomes evident that the ship will sink. All life-saving equipment is occupied and a sailor, weighing 800 N, is hoping to save himself in the shark-infested waters by floating on top of one of the containers. Four containers with total weights of 2,000, 10,000, 60,000 and 90,000 N, respectively, are available. Assume that the seawater specific gravity is 1.025.

Which container would you advise the sailor to choose?

Contributed by Stavros Tavoularis, Department of Mechanical Engineering, University of Ottawa, Ottawa, Canada.