(17%) Problem 3: Suppose a car travels 102 km at a speed of 28.5 m/s, and uses 2
ID: 1775918 • Letter: #
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(17%) Problem 3: Suppose a car travels 102 km at a speed of 28.5 m/s, and uses 2.5 gal of gasoline in the process. Only 30% of the gasoline goes into useful work to keep the car moving at a constant speed. In this problem you may assume that 1 gallon of gasoline produces 12x 108 J of energy 50% Part (a) What is the force exerted, in newtons, to keep the car moving at constant speed? Grade Summary 0% 100% Potential sin) cotan0 | asinOacos0 | tano-lal.(M71819 4 5 6 Submissions Attempts remaining: 10 (5% per attempt) detailed view cos() "1 23 atan acotan0 sinh0 cosh0 tan cotanh0 °Degrees Radians Submit I give up! Feedback: 3% deduction per feedback. Hits: 2% deduction per hint. Hints remaining: 1 50% Part (b) If the required force is directly proportional to the speed that the car travels at how many gallons will be used to drive 102 km at a speed of 275 m/s? Allcontent © 2017 Expert TA.ucExplanation / Answer
Total Energy from Fuel = 2.5*1.2 x 108 = 3 x 108 J
Energy loss in friction = 30% of total = 9 x 107 J
E = F*d
F = E/d
F = 9 x 107 J/102000m
F = 882.35 N
Ff = - 882.35 N (there is no other force on tires expect friction)
Part B:
F1/V1 = F2/V2
F2 = F1*(V2/V1)
F2 = 882.35 N(27.5 m/s /28.5 m/s)
F2 = 851.4 N
E2 = F2*d2
E2 = 851.4*102000m
E2 = 86842105.3 J
Fuel used = 86842105.3 J*(1/1.2 x 108)*(100/30)
Fuel used = 2.41 gallons
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