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Energy of a system

# Energy of a system - adamkiewicz(ja28724 Energy of a system...

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adamkiewicz (ja28724) – Energy of a system – Morozova – (11102) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points This question is typical on some driver’s li- cense exams: A car moving at 43 km / h skids 13 m with locked brakes. How far will the car skid with locked brakes at 107 . 5 km / h? Correct answer: 81 . 25 m. Explanation: 107 . 5 km / h 43 km / h = 2 . 5 At 2 . 5 times the speed, it has 6 . 25 times the KE parenleftbigg 1 2 m v 2 parenrightbigg and will skid 6 . 25 times as far: 81 . 25 m. Since the frictional force is about the same in both cases, the distance has to be 6 . 25 times as great for 6 . 25 times as much work done by the pavement on the car. 002 10.0 points The Joule and the kilowatt-hour are both units of energy. 11 . 9 kW · h is equivalent to how many Joules? Correct answer: 4 . 284 × 10 7 J. Explanation: 1 W = 1 J / s 11 . 9 kW · h = (11 . 9 kW · h) · 1000 W kW · 3600 s 1 h = 4 . 284 × 10 7 W · s = 4 . 284 × 10 7 J . 003 (part 1 of 5) 10.0 points A 18 . 9 kg block is dragged over a rough, hor- izontal surface by a constant force of 118 N acting at an angle of angle 31 above the hor- izontal. The block is displaced 48 . 2 m, and the coefficient of kinetic friction is 0 . 203.

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