A cylindrical ram

$7($of radius $R$ y legth $L)$ with densuty ${}_s$ is introduced at constant speed $U$ concentricall into a cylindrical well $($of radius $R$ and legthL $)$ open to the atmosphere, which contains a fluid inside. Viscous $($newtonian$)$ of density $$ and viscosity $.$ Determine the force $F(l)$ that must be applied to the ram as function of the length of the ram introduce into the $0lL.$ Assume thet viscous effects are important and that the flow in the annular region can be approximated to steady, one$-$dimensional flow. For the calculation of the applied force, do not forget to consider both the viscous force and the pressure force. Any assumption made, justify it in writing