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

`rArr eta=2.5xx10^(-2) kg -sec//m^(2)`