Solutions
Concept:
The drag force acting on a plate is given by:
Where,
V is the stream velocity
A is the project area over the plate
CD is the drag coefficient or average skin friction coefficient
Now, CD ∝ √X ⇒ CD = C√X, where C is constant.
Calculation:
Let the length of plate is L, then upstream length is L/2 and downstream length is also L/2 as shown in the figure:

Consider a small strip of length ‘dx’ at a distance ‘x’ from leading edge of the plate. Let width of strip is B and drag force acting on this strip is dF.
Projected area strip is dA = B⋅dx
Ρ, V, B, C are constant = K (say)
Let FAB and FBC are the drag forces on portion AB and BC respectively.
For AB portion: x varies from 0 to
; So, total drag force on AB is:
For BC: x varies from L/2 to L,
Now,
The desired ratio is,