A cubical block of side 'a' and density '$\mathrm{\rho }$' 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)

• A

  $\frac{\mathrm{\rho agtsin\theta }}{\mathrm{v}}$

• B

  $\frac{{\mathrm{\rho agt}}^2\mathrm{sin\theta }}{\mathrm{v}}$

• C

  $\frac{\mathrm{v}}{\mathrm{\rho agtsin\theta }}$

• D

  none of these