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A space 2.5cm wide between two large pla...

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 `0.5m//sec` is 1N. The coefficient of vescosity in `kg-s//m^2` is:

A

`5xx10^(-2)`

B

`2.5 xx10^(-2)`

C

`1xx10^(-2)`

D

`7.5 xx10^(-2)`

Text Solution

Verified by Experts

The correct Answer is:
B
Velocity gradient `=0.5/(2.5/2xx10^(-2))`
as force on the plate due to viscocity is from upper as well as lower portion of the oil, equal from each part,
Then`F=2 etaA(dv)/(dz) =2xxetaxx(0.5)0.5/(1.25xx10^(-2))`

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