GATE 2019 ME (ME2) – Question 54
A sports car has drag coefficient 0.1 with windows and roof closed, and 0.8 with them open. Closed, it travels at 44 km/h. Find open-condition speed at the same aerodynamic power (km/h), to two decimal places. Density and frontal area remain constant.
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Correct answer: 21.90 to 22.20
Explanation
Aerodynamic power is proportional to $C_Dv^3$. Thus $v_2=44(0.1/0.8)^{1/3}=\mathbf{22.00}$ km/h.