lecture23[1] - 1 Physics 1D03 Mechanical Energy Serway 8.1...

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Unformatted text preview: 1 Physics 1D03 Mechanical Energy Serway 8.1 – 8.4 • More examples • Non-conservative forces Practice problems: Serway chapter 8, problems 7, 15, 23, 65, 69 Physics 1D03 Mechanical Energy E = K + U = K + U gravity + U spring + ... Mechanical energy is conserved by “conservative” forces; the total mechanical energy does not change if only conservative forces do work. 2 Physics 1D03 - Lecture 23 Example A 30-kg dog is tied to a post by a long nylon rope. The rope obeys Hooke’s Law, with a spring constant k = 600 N/m and a breaking strength of 2400 N. Each day a physicist bicycles past, and the dog experiments with breaking the rope by running at top speed and letting the rope stop him. How fast would he have to run to break the rope? (Hint: consider the energy required to break the rope.) v Physics 1D03 - Lecture 23 Quiz The dog’s owner replaces the nylon rope with a thin steel cable which has a spring constant 9 times as large, but the same breaking strength (2400 N). To break the cable, the dog will have to run: a) at the same speed as before b) 3 times as fast c) 9 times as fast d) 1/3 as fast 3...
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lecture23[1] - 1 Physics 1D03 Mechanical Energy Serway 8.1...

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