A space `2.5cm` wide between two large plane surfaces is filled with oil. Force required to drag a very thin plate of area `0.5m^2` just midway the surfaces at a speed of `0.5(m)/(sec)` is `1N`. The coefficient of viscosity in `kg-(s)/(m^2)` is:

Options

A. `5xx10^-2`
B. `2.5xx10^-2`
C. `1xx10^-2`
D. `7.5xx10^-2`

Answer

B

Explanation

Velocity gradient`=(0.5)/((2.5)/(2)xx10^-2)`
as force on the plate due to viscosity is from upper as well as lower portion of the oil, equal from each part,
Then `F=2etaA(dv)/(dz)=2xxetaxx(0.5)(0.5)/(1.25xx10^-2)`
`implieseta=2.5xx10^-2kg-(sec)/(m^2)`