A cube-shaped box drops from a ship into the sea. It reaches the water with its bottom face exactly level with the sea surface. The box starts to sink, is then completely underwater, and afterwards continues to move further down into the sea. While the box is descending, its bottom face remains parallel to the sea surface at all times. Which graph shows best how the upthrust on the box changes with the depth of its bottom face below the sea surface?
Physics 9702 · AS & A Level · Density and pressure