In a laminar flow the velocity of the liquid in contact with the walls of the tub is

The correct answer is Zero.

Step-by-step Explanation:

1. Concept of Laminar Flow:
Laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption between the layers. In this type of flow, the velocity, pressure, and other flow properties at each point in the fluid remain constant over time.

2. The No-Slip Condition:
When a viscous fluid flows past a solid boundary (such as the inner wall of a tube), the fluid molecules immediately next to the solid surface stick to it due to adhesive forces between the fluid molecules and the solid wall. This physical phenomenon is known as the no-slip condition.

3. Velocity Distribution:
Because of the no-slip condition, the layer of liquid in direct contact with the stationary wall of the tube has the same velocity as the wall itself. Since the tube walls are at rest, the velocity of this boundary layer of liquid is:
$v=0$

As we move radially inward from the walls towards the center of the tube, the velocity of the liquid layers increases, reaching its maximum value at the central axis of the tube. Therefore, the velocity of the liquid in contact with the walls of the tube is zero.