Question

A cubic box has a volume of 1.0 cubic meters and a mass of 2000 kg. A crane’s cable holds up the box, initially with the box being submerged such that its top is 1.0 m below the surface of a pool of still water. At a constant rate, the box is lifted until its bottom is 1.0 m above the water. Sketch a graph of the force the crane cable exerts on the box versus distance for the center of the box being 1.0 m below to 1.0 m above the surface. [Don’t worry about the starting and stopping of the box’s movement.]

Answer 1

There are few things that needs to be considered constant or non-influential. It is like the pressure change with height,

THe forces acting on the box is weight downward, buoyant force upward, Lift force (tension in the cable) upward and net force is upward. Now we should be deriving the graph for the net force and distance of travel (lift). We should have clarity that that if the applied force (tension in the string) is same through out (box in water and out of water) then net force when the box is in water is less than the net force when the box is out of water though the distance of lift is same in both cases.