Question

An automobile with projected area $2.6m^2$ is running on a road with a speed of 120 km per hour. The mass density and the kinematic viscosity of air are $1.2kg/m^3$ and $1.5\times {10}^{-5}{m}^2/s$, respectively. The drag coefficient is 0.30.
The drag force on the automobile is

• A. 620 N
• B. 600 N
• C. 580 N
• D. 520 N

Answer 1

The correct option is D 520 N

The drag force on the automobile may be given as
$F_D=C_{D}A\times \frac{\rho V^2}{2}$
Here, $C_D=0.30,A=2.6m^2,\rho =1.2kg/m^3,V=120kmph$
$\therefore F_D=0.30\times 2.6\times \frac{1.2\times (120\times 1000{)}^2}{2\times (60\times 60{)}^2}$
$=520N$