The aerodynamic drag on a car depends on the "shape" of the car. For example, the car shown in Fig. P9.42 has a drag coefficient of 0.35 with the windows and roof closed. With the windows and roof open, the drag coefficient increases to 0.45. With the windows and roof open, at what speed is the amount of power needed to overcome aerodynamic drag the same as it is at \(65 \mathrm{mph}\) with the windows and roof closed? Assume the frontal area remains the same. Recall that power is force times velocity.

Figure P9.42

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Windows and roof closed: CD = 0.35 Windows open; roof open: Cp = 0.45