Question

18. The boundary layer thickness at a distance
of 1 m from the leading edge of a flat
plate, kept at zero angle of incidence to
the flow direction, is 0.1 cm. The velocity
outside the boundary layer is 25 m/ sec.
The boundary layer thickness at a distance
of 4 m is​

Answer 1

the answer is 0.2 cms

the explanation is there

Answer 2

For laminar flow, the thickness of the boundary layer is inversely proportional to the square root of Reynold's number.

The number Reynold's, Re =D stands for hydraulic diameter.

V stands for velocit  = volumetric density = viscosity coefficient

Therefore, As a result, lighter fluid will have a thicker boundary layer at a given place than a denser fluid.

Note: In the case of turbulent flow,

In laminar flow, the boundary layer thickness varies with density, i.e., if the fluid is lighter, the boundary layer thickness will be greater.