The drag coefficient of a car of design condition 60 kmph is to be determined experimentally in a large wing tunnel in a full scale test. The frontal area of the car is $3 m^{2}$ . If the force acting on the car in flow direction is measured to be 100 N, then the drag coefficient of car is (take $ρ_{a i r} = 1.25 k g / m^{3}$ )

0.15

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0.2

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0.25

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0.3

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Solution

The correct option is B 0.2
We know
$F_{D} = C_{D} \frac{ρ A V^{2}}{2}$

Given drag force

$F_{D} = 100 N$

$ρ = 1.25 k g / m^{3}$

$A = 3 m^{2}$

$V = 60 \times \frac{5}{18} m / s$

$= 16.67 m / s$

$∴ 100 = C_{D} \times \frac{1.25 \times 3 \times {16.67}^{2}}{2}$

$C_{D} = 0.1919 ≃ 0.2$

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The correct option is B 0.2We know FD=CDρAV22 Given drag force FD=100 N ρ=1.25 kg/m3 A=3 m2 V=60×518m/s =16.67 m/s ∴100=CD×1.25×3×16.6722 CD=0.1919≃0.2

The correct option is B 0.2
We know
$F_{D} = C_{D} \frac{ρ A V^{2}}{2}$

Given drag force

$F_{D} = 100 N$

$ρ = 1.25 k g / m^{3}$

$A = 3 m^{2}$

$V = 60 \times \frac{5}{18} m / s$

$= 16.67 m / s$

$∴ 100 = C_{D} \times \frac{1.25 \times 3 \times {16.67}^{2}}{2}$

$C_{D} = 0.1919 ≃ 0.2$