A cubical block of side `a` and density `rho` slides over a fixed inclined plane with constant velocity `v`. There is a thin film of viscous fluid of thickness `t` between the plane and the block. Then the coefficient of viscosity of the thin film will be: (Acceleration due to gravity is g)

Options

A. `(rhoagtsintheta)/(v)`
B. `(rhoagt^2sintheta)/(v)`
C. `(v)/(rhoagtsintheta)`
D. none of these

Answer

A

Explanation

Viscous force `=mgsintheta`
`etaA(v)/(t)=mgsintheta` or `etaa^2(v)/(t)=a^2rhogsintheta`
`eta=(trhogsinthetaa)/(v)`