need help with 5.3, the answers for 5.1 and 5.2 are 27.6kW and 25.9 kW A car is
ID: 1328438 • Letter: N
Question
need help with 5.3, the answers for 5.1 and 5.2 are 27.6kW and 25.9 kW
A car is traveling along a highway at 65 miles per hour. The road is horizontal (0% slope). If the wind resistance and rolling resistance at the wheels creates a combined resistive force of 950 N. what is the power (kW) developed at the rear wheels? How much power (kW) must the car engine in problem 5.1 develop if the overall mechanical efficiency of the transmission and drive train is 94%? Assume the car engine in problem 5.1 is operated on gasoline with an energy content of 113.500 Btu's per gallon, and that the thermal efficiency of the spark ignition engine and drive train is 28.6%. What is the fuel efficiency of the car in miles per gallon?Explanation / Answer
Here ,
5.1
speed of car, v = 65 miles/hr
v = 65 * 1609/3600
v = 29.05 m/s
Power = speed * force
Power = 29.05 * 950
Power = 27600 W
power devloped by the wheels is 27.6 kW
5.2)
power by car engine = 27.6/0.94
power by car engine = 29.4 kW
the power by car engine is 29.4 kW
5.3)
energy produced per gallon of gasoline = 1.055 * 113500 KJ
energy produced per gallon of gasoline = 119742.5 KJ
now , energy reaching the transmisison = 119742.5 * 0.286
energy reaching the transmisison = 34246.355 KJ
time to consume this energy = 34246.355/29.4
time to consume this energy = 1.1658 hour
distance travelled = 1.1658 * 65
distance travelled = 75.7 miles
the fuel efficiency of car is 75.7 miles per gallon
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