Spherical balls of radius R are falling in a viscous fluid of 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