Consider a 1200 kg car presenting a front-end area 2.60 m2 and having a drag coefficient 0.385. It can achieve instantaneous acceleration 3.00 m/s2 when its speed is 10.0 m/s. Ignore any force of rolling resistance. Assume that the only horizontal forces on the car are static friction forward exerted by the road on the drive wheels and resistance exerted by the surrounding air, with density 1.20 kg/m3. (a) Find the friction force exerted by the road. (b) Suppose the car body could be redesigned to have a drag coefficient of 0.165 If nothing else changes, what will be the car's acceleration? (c)Assume that the force exerted by the road remains constant. Then what maximum speed could the car attain with D = 0.385?

An aeroplane has a rectangular planform wing with a span of 12 m and a chord of 2 m. The aircraft is flying at cruising speed of 62 m/s at an altitude of 3,200 m. Assume that the skin-friction drag on the wing can be approximated by the drag on a flat plate of the same dimensions at 0° incidence. Calculate the skin-friction drag and the maximum boundary layer thickness assuming (i) a completely laminar flow, and (ii) a completely turbulent flow. Assume μ = 1.63.10-5 N s/m², p = 0.89 kg/m³. Then, calculate the skin-friction drag accounting for transition at Recr= 5.105. What would the drag benefit be if transition was delayed to a Reynolds number of 106? What reduction in a propeller engine power would this imply in the cruise condition, assuming a propeller efficiency of 0.88?

and power for part b

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