The coefficient of viscosity of an ideal fluid is

When stirring with a spoon is stopped in milk,it comes to rest after some time. Why?

$A$ metal block of base area $0.2\; m^{2}$ is connected to a $0.02\; kg$ mass via a string that passes over an ideal pulley as shown in the figure. $A$ liquid film of thickness $0.6\; mm$ is placed between the block and the table. When released,the block moves to the right with a constant speed of $0.17\; m/s$. The coefficient of viscosity of the liquid is:

$A$ liquid having a coefficient of viscosity $0.02 \, \text{decapoise}$ is filled in a container of cross-sectional area $20 \, m^2$. If the viscous drag between two adjacent layers in flowing is $1 \, N$, then the velocity gradient is ........ $s^{-1}$.

Water is flowing on a horizontal fixed surface,such that its flow velocity varies with $y$ (vertical direction) as $v = k \left( \frac{2y^2}{a^2} - \frac{y^3}{a^3} \right)$. If the coefficient of viscosity for water is $\eta$,what will be the shear stress between the layers of water at $y = a$?

$A$ good lubricant should have