What is the definition of net upward force?

[Palak Verma]

To keep the can immersed, an external downward force is needed to balance the net upward force(=F'b-W).

 

[Kilgour22]

You may want to expand on your question.

 

[Palak Verma]

F'b means maximum upthrust.

 

[CWatters]

The expression "net force in direction x" means the sum of all forces, or components of forces, that act in direction x. If the sum of forces acting in the x direction is zero then the object isn't accelerating in the x direction.

 

[Chestermiller]

To keep the can immersed, an external downward force is needed to balance the net upward force(=F'b-W).

F'_b is the buoyant force (due to hydrodynamic pressure) on the can, and W is the weight of the can and its contents. The "net upward force" as used in the present context is the buoyant force minus the weight.

Chet