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

• A. \[\frac{\eta k}{a}\]
• B. \[\frac{\eta }{ka}\]
• C. \[\frac{\eta a}{k}\]
• D. None of these