HW12 - schneiter (tcs639) HW12 Ross (89152) 1 This...

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Unformatted text preview: schneiter (tcs639) HW12 Ross (89152) 1 This print-out should have 8 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points Betty weighs 440 N and she is sitting on a playground swing seat that hangs 0 . 48 m above the ground. Tom pulls the swing back and releases it when the seat is 0 . 79 m above the ground. The acceleration of gravity is 9 . 8 m / s 2 . How fast is Betty moving when the swing passes through its lowest position? Correct answer: 2 . 46495 m / s. Explanation: The swing moves from the highest position to the lowest. By conservation of energy, U o + K o = U f + K f mg h o + 0 = mg h + 1 2 mv 2 2 g h o = 2 g h + v 2 v = radicalbig 2 g h o- 2 g h = radicalbig 2 g ( h o- h ) = radicalBig 2 (9 . 8 m / s 2 ) (0 . 79 m- . 48 m) = 2 . 46495 m / s . 002 (part 2 of 2) 10.0 points If Betty moves through the lowest point at 1 . 4 m / s, what is the magnitude of the work done on the swing by friction? Correct answer: 92 . 4 J. Explanation: This time the swing does work against fric- tion, so U o + K o- W fr = U f + K f mg h o + 0- W = mg h + 1 2 mv 2 1 W = mg h o- mg h- 1 2 mv 2 1 W = F w h o- F w h- 1 2 F w g v 2 1 = (440 N) (0 . 79 m)- (440 N) (0 . 48 m)- 1 2 parenleftbigg 440 N 9 . 8 m / s 2 parenrightbigg (1 . 4 m / s) 2 = 92 . 4 J . 003 10.0 points A block of mass 0 . 16 kg is placed on a verti- cal spring of constant 7467 N / m and pushed downward, compressing the spring 0 . 08 m....
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HW12 - schneiter (tcs639) HW12 Ross (89152) 1 This...

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