Question

Along a streamline.
A. The velocity of a fluid particle remains constant
B. The velocity of all fluid particles crossing a given position is constant
C. The velocity of all fluid particles at a given instant is constant
D. The speed of the fluid particle remains constant

Answer 1

The streamlined flow is also known as a laminar flow.
The streamline flow is described as there is no turbulence and the fluctuations in velocity. A streamline is a path traced by a particle in a flow.

Complete step by step solution:
The streamlined body has a very small contact with the fluid which it is passing through. Hence in the form of heat it loses energy.
If the streamline forms a closed curve it represents the fluid particles cannot pass the boundary.
Streamline flow is a kind of flow where the fluid is flowing separately without mixing. The velocity of each fluid particle flowing will remain constant with time in a streamlined flow.
In the case of low fluid velocities, the fluid will flow without any sort of lateral mixing because of the lack of turbulent velocity fluctuations. The fluid particles tend to follow a particular order where the movement or motion of fluid particles will be based on particles flowing in a straight line parallel to the pipe wall.
$AV =$constant. [here, $A =$ cross-sectional area, $V =$velocity ]
It means the fluid particles are constant at a particular cross-section. Hence we said the velocity of a fluid particle is constant when crossing a position.
So, the answer is, option (B).

Note:
The curve that is tangent to the velocity vector is known as a streamlined curve.
The streamline is the graphic representation that shows how the fluid gets passed at any instant.
When the velocity at any point is constant or varies regularly is called a streamline flow.