$2($a$).$ A $12-$kg cube slides down an incline plane making an angle of $30$ with the horizontal. A fluid

film $0\mathrm{.}1mm$ thick separates solid and surface. The fluid viscosity is $0\mathrm{.}04N.\frac{s}{m^2}.$ Assuming the

velocity in the film is linear, find the terminal velocity of the block. The area of the cube in contact

with the film is $0\mathrm{.}25m^2.[$Problem $1\mathrm{.}20$ Streeter, Wylie & Bedford$]$