Question

In static fluid
A. Resistance to shear stress is small.
B. Fluid pressure is zero.
C. Only normal stress can exist.
D. Linear deformation is small.

Answer 1

Hint: The fluid in which the net force is zero is considered to be static fluid. This means the fluid moving with constant velocity can be considered as static fluid. This also includes a stationary fluid. i.e. zero velocity. Non-ideal fluids (the fluids in which viscosity and turbulence present) will never flow with constant velocity due to the presence of non-zero shear forces. But in some cases, like the fluid in a tank moving with constant acceleration is considered as the static case with the assumption that the internal motion within the fluid is negligible.

Formula used:
${{P}_{static\ fluid}}=\rho gh$

Complete step by step answer:
In a static fluid, the net force on the fluid is zero. Shear stress is defined as the force tending to cause deformation of material by slippage between the layers or parallel to the imposed stress. If there is small resistance to shear stress then the fluid will not be a static fluid. The static fluid pressure is the pressure exerted by a static fluid column and will depend only upon the depth of the fluid, the density of the fluid, and the acceleration due to gravity. And is represented by
${{P}_{static\ fluid}}=\rho gh$, where $\rho =\text{ density of liquid,}h=\text{height of water column}$. So the static fluid pressure is not zero.
For a static fluid, the only stress is the normal stress because by definition a fluid subjected to shear stress must deform and undergo motion. So normal stress exists.
For static fluid, there will be large linear deformation because there exists no viscous force for static fluid.
Hence, the correct answer is option C.

Note:
The fluid on which there's no tangential shear force is acting is often termed as static fluid. If there's any tangential shear force then fluid will start moving or the layers of fluid will start slipping, which can cause the motion of the fluid. A fluid moving with constant velocity could also be termed as static fluid.