Problem 8.65 PartA Constants | Periodic Table A driver notices that her 1080 kg

Question

Problem 8.65 PartA Constants | Periodic Table A driver notices that her 1080 kg car slows down from 98 km/h to 62 km/h in about 6.0 s on the level when it is in neutral. Approximately what power (in watts) is needed to keep the car traveling at a constant 80 km/h? Express your answer using two significant figures Submit RequestAnswer Part B Approximately what power (in hp) is needed to keep the car traveling at a constant 80 km/h? Express your answer using two significant figures hp Submit RequestAnswer

Explanation / Answer

Problem 8.65

Part A:

98 km/hr = 98 x 1000/3600 = 27.222 m/s

62 km/hr = 62 x 1000/3600 = 17.222 m/s

Decrease in Kinetic Energy of car = 1/2m (27.2222) - 1/2 m(17.2222)

Delta KE = 0.5 x 1080 x (741.04 - 296.60) = 239995.347 J

Time taken t = 6.0 s

Hence, power required must be equal to rate of decrease of KE = 239995.347/6.0 = 3999.22 W

Required power P = 3999.22 W for keeping constant speed.

Part B,

One HP = 746 Watt

Hence, 3999.22 Watt in HP = 3999.22/746 = 53.62 Horse Power

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