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
inversely proportional to both radius $R$ and velocity $v$
directly proportional to both radius $R$ and velocity $v$
directly proportional to $R$ but inversely proportional to $v$
inversely proportional to $R,$ but directly proportional to velocity $v$
