3.9 A passenger car weighs 20.75 kN (4665 lb). Its frontal area is 2.02 m2 (21.7

Question

3.9 A passenger car weighs 20.75 kN (4665 lb). Its frontal area is 2.02 m2 (21.74 ft) and the aerodynamic drag coefficient is 0.36. The coefficien of rolling resistance is given by f0.0136+0.4 x 10-7 V2, where V is the speed of the car in kilometers per hour (A) Estimate the maximum engine power required to accelerate the car at a constant rate from standstill to a speed of 97 km/h (60 mph) in 8 s, on a level road and with zero wind speed. The mass factor m at the highest gear of the transmission is 1.08 and the average transmission efficiency is 0.9. (B) Estimate the engine power required for cruising at a constant s ene of 97 km/h (60 mph). Compare the power requirement for c with that for acceleration under the condition described in (A) ruising (C) If the weight of the car is reduced by 20% (by using high-strength. lightweight material and advanced design and pr niques), estimate the maximum engine power required Compart eration under the same condition as that described in ( the power requirement for weight reduction of 20 the original weight of the car. oduction tech- accer A). % with that for

Explanation / Answer

When car runs friction drag and weight acts as a resistance to flow frontal area is given so we can easily calculate drag force rolling resistance is also given so rolling friction and power required to overcome that friction can be calculated while calculating acceleration we have to make sure that we consider both resistance and then use equation of motion

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