Question

A smooth flat plate is in a parallel flow stream. The ratio of the drag over the upstream half of the plate to that over the entire plate is ... Assume the average skin friction coefficient is proportional to $(R{e}_x{)}^{-1/2}$.

• A. 0.707

Answer 1

The correct option is A 0.707

Reynolds number,
$Re=\frac{\rho Vx}{\mu }$
$given{C}_{f}x\propto \frac{1}{\sqrt{x}}$
$\Rightarrow \frac{F_{D}1}{F_{D}2}=\frac{\sqrt{x_2}}{\sqrt{x_1}}=\frac{\sqrt{l/2}}{\sqrt{l}}=\frac{1}{\sqrt{2}}$