The drag coefficient for a newly designed hybrid car is predicted to be 0.21. The cross-sectional area of the car is 30 ft2 . Determine the aerodynamic drag on the car when it is driven through still air at 55 mph.

D = 1311.94 lb/ft

Explanation:

We are given the velocity as;

V = 55 mph.

First of all, let's convert it to ft/s

V = 55 × (5280/3600) ft/s

V = 80.67 ft/s

The equation for the aerodynamic drag force on the car is given as;

D = C_d•½ρ•V²•A

Where;

C_d is drag coefficient = 0.21

ρ is density of air

V is velocity = 80.67 ft/s

A is area 55 ft²

Now, from tables, the density of air under S.T.P condition is 1.225 kg/m³. Converting to lb/ft³ gives; 0.0624 lb/ft³

Plugging in the relevant values, we have;

D = 0.21•½•0.0624•80.67²•30

D = 1311.94 lb/ft

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