A drop of water of radius `r` is falling rhough the air of coefficient of viscosity `eta` with a constant velocity of `v` the resultant force on the drop is

Spherical balls of radius R are falling in a viscous fluid of viscosity eta with a velocity v. The retarding viscous force acting on the spherical ball is

Spherical balls of radius 'R' are falling in a viscous fluid of viscosity 'eta' with a velocity 'v'. The retarding viscous force acting on the spherical ball is

Spherical balls of radius 'R' are falling in a viscous fluid of viscosity 'eta' with a velocity 'v'. The retarding viscous force acting on the spherical ball is

Spherical balls of radius 'R' are falling in a viscous fluid of viscosity 'eta' with a velocity 'v'. The retarding viscous force acting on the spherical ball is:

Spherical balls of radius 'R' are falling in a viscous fluid of viscosity 'eta' with a velocity 'v'. The retarding viscous force acting on the spherical ball is