Viscosity,Fluid flow and terimal velocity

[ChunkymonkeyI]

Homework Statement

When does Fb(Buoyancy force) equal the drag force(FD)?
and Fb+FD=Fg

Homework Equations

Fb=density of water times volume of water times 9.80 m/s^2
FD=6pi times viscosity times radius times v
Fg=mg

The Attempt at a Solution

All ik is the solid has 2 be in the air going to the water but idk how 2 really prove that please help me

 

[RTW69]

This problem is really confusing. Do we have a ball falling in water? Not sure what is going on here.

 

[ehild]

It is a sphere of radius r moving with speed v in a fluid of viscosity η. The drag force is F_D=6πηrv.
The buoyant force is F_B=ρVg, where ρ is the density of the liquid and V is the volume of the sphere.

ehild

PS: ChunkymonkeyI, what did you mean: "All ik is the solid has 2 be in the air going to the water but idk how 2 really prove that please help me" We use English here.