Q1: A static fluid can not have

ANS:C - non-zero shear stress.

A static fluid refers to a fluid that is at rest or in equilibrium, meaning it is not flowing or deforming. In the context of fluid mechanics, a static fluid is characterized by certain properties:

1. Zero Shear Stress: In a static fluid, there is no motion or deformation occurring, so the shear stress is indeed zero. Shear stress arises from the force applied tangentially to a surface and is responsible for causing the fluid to flow or deform. In a static fluid, there is no such force acting tangentially, resulting in zero shear stress.
2. Positive Normal Stress: Normal stress refers to the force applied perpendicular to a surface. In a static fluid, there can indeed be positive normal stress acting due to the weight of the fluid or any external pressure applied to it. This normal stress is essential for maintaining the fluid in equilibrium, balancing the forces exerted on it.
3. Non-zero Shear Stress: As mentioned earlier, a static fluid by definition does not exhibit flow or deformation. Hence, it cannot have non-zero shear stress. Shear stress arises from the tendency of fluid layers to slide past each other, causing deformation or flow. In a static fluid, there is no such motion occurring, so the shear stress remains zero.