block slide down

[logistic_guy]

here is the question

A block slides down a long, straight, inclined wall at speed $\displaystyle V$, riding on a thin film of oil of thickness $\displaystyle h$ as shown. The weight of the block is $\displaystyle W$, and its surface area in contact with the oil film is $\displaystyle A$. Suppose $\displaystyle V$ is measured, and $\displaystyle W, A,$ angle $\displaystyle \alpha,$ and viscosity $\displaystyle \mu$ are also known. Oil film thickness $\displaystyle h$ is not known. Generate an exact analytical expression for $\displaystyle h$ as a function of the known parameters, $\displaystyle V, A, W, \alpha,$ and $\displaystyle \mu$.




my attemb
i assume force of gravity pulling block down and i also assume tiny friction force in the opposite side
$\displaystyle W\sin \alpha - F_{r} = ma$
this question is written very bad. it don't tell me if there is friction. it also don't tell me if speed constant or change
i'll assume there is no acceleration
$\displaystyle W\sin \alpha - F_{r} = 0$
this expression tell me speed and surface area and viscosity is part of friction
from previous lesson i remember speed and viscosity and oil thickness is part of shear stress in Couette flow
but in quesition it don't tell anything about shear stress or Couette flow
do i have to assume this or i'm wrong?
very bad author, it write poorly question for advance engineering