$A$ square plate of $0.1 \; m$ side moves parallel to a second plate with a velocity of $0.1 \; m/s$, both plates being immersed in water. If the viscous force is $0.002 \; N$ and the coefficient of viscosity is $0.01 \; \text{poise}$, the distance between the plates in $m$ is:

Explain velocity gradient and coefficient of viscosity and give their units.

$A$ flat plate of area $10 \, cm^2$ is separated from a large plate by a layer of glycerine $1 \, mm$ thick. If the coefficient of viscosity of glycerine is $20 \, \text{poise}$, the force required to keep the plate moving with a velocity of $1 \, cm/s$ is .......... $dyne$.

$A$ metal plate of area $10^{-2} \,m^2$ rests on a layer of castor oil,$2 \times 10^{-3} \,m$ thick,whose coefficient of viscosity is $1.55 \,Ns\, m^{-2}$. The approximate horizontal force required to move the plate with a uniform speed of $3 \times 10^{-2} \,ms^{-1}$ is (in $N$)

$A$ metal block of base area $0.20\,m^2$ is placed on a table,as shown in the figure. $A$ liquid film of thickness $0.25\,mm$ is inserted between the block and the table. The block is pushed by a horizontal force of $0.1\,N$ and moves with a constant speed. If the viscosity of the liquid is $5.0 \times 10^{-3} \,Pa-s$,the speed of the block is $.........\times 10^{-3}\,m/s$.

The coefficient of viscosity for hot air is