Question

Which among the following is the correct formula for drag?

(a) D = Cd * A * 0.5 * r * V^2

(b) D = Cd * A * 0.5 * r * V*2

(c) D = Cd * A * 0.5 * r * V/2

(d) D = 0.5 * r * V

The question was posed to me in an interview for job.

This key question is from Types of Forces Acting in Moving Fluid in chapter Dimensional and Model Analysis of Fluid Mechanics

Answer 1

The correct answer is (a) D = Cd * A * 0.5 * r * V^2

Easiest explanation: The drag force acts in the opposite direction to that of the relative flow velocity. It acts in the opposite direction with respect to a surrounding fluid flow. Thus, the correct option is D = Cd * A * 0.5 * r * V^2.