Question

Fluid is a substance that
A. cannot be subjected to shear force
B. always expands until it fills any container
C. has the same shear stress at a point regardless of its motion
D. takes the shape of the container

Answer 1

We know that fluid is a substance, which is the ability of a material to flow. This is often seen in gases and liquids, thus clearly, we can say that the particles of the fluid are always in motion. We also know that stress is the force per unit area i.e. $stress=\dfrac{\text{force}}{\text{area}}$.

Formula usd: $stress=\dfrac{\text{force}}{\text{area}}$

Complete step-by-step solution:
We know that shear stress is a form of stress, it is the external force applied per unit area of the given fluid. We also know that an external force always affects the inertia of the object. We know that a fluid can be subjected to stress, like expansion or compression, then we can say that fluid can be subjected to shear stress also. Thus option A is not the correct answer.
Depending on the stress, the fluid can expand or compress, thus clearly option B is not the correct answer.
Then, we can say that at different points of the fluid, different shear stress acts on the fluid. Hence clearly, option C is not the correct answer.
We also know that fluids, change their shapes when an external force acts on it, then we can say that option D is the correct answer.

Note: Fluids are a mixture of liquids and gases. Also due to the weak intermolecular forces, both are free to flow, also they take up the shape of the container in which they are kept. Thus we can say that both when subjected to some external force, change their shape and volume.