Force on a sphere in flowing water and velocity of water

[come2ershad]

Homework Statement

The problem has been attached with this post.

Homework Equations

Equation given below.

The Attempt at a Solution

The forces on the sphere could be due to gravity and the buoyancy force.
((pi*d^3)/6)×ρ(water)×g=mg
From this I can find the mass of the sphere in terms of the density of fluid.
Then Fv = m (dv/dt). But, I am stuck here. How should I proceed? Is my approach correct?

 

[come2ershad]

Also, though viscosity of water is given in the problem, i doubt if there would be any drag force on the sphere since the sphere doesn't seem to be moving significantly through the water. Please throw some light on this concept too.