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Unformatted text preview: Lecture 11 Purdue University, Physics 220 1 Lecture 11 Potential Energy and Energy Conservation Textbook Sections 6.4  6.8 PHYSICS 220 Lecture 11 Purdue University, Physics 220 2 Exam I each problem = 10 pts > 130 pts total (raw) mean = 85 (or 98 scaled) pts or ~65% std dev = 24 (or 28 scaled) pts Lecture 11 Purdue University, Physics 220 3 Overview Last Lecture Energy is Conserved Work = Transfer of energy using force Can be positive, negative or zero W = F d cos Kinetic Energy (Motion) K = m v 2 Work = Change in Kinetic Energy W = K Today Potential (Stored) Energy Power Lecture 11 Purdue University, Physics 220 4 Potential Energy Work done by gravity independent of path W g = mg (y f y i ) =  U g Define U g = mgy Only the difference in potential energy is physically meaningful, i.e., you have the freedom to choose the reference (or zero potential energy) point. Works for any CONSERVATIVE force Lecture 11 Purdue University, Physics 220 5 Work by Variable Force W = F x x Force Distance Work Force Distance F = k x Work Work is the area under the F vs x plot U s = 1/2 k x 2 Spring: F = k x Area = k x 2 =W spring Potential Energy: Lecture 11 Purdue University, Physics 220 6 WorkEnergy with Conservative Forces Move work by conservative forces to other side If there are NO nonconservative forces Work Energy Theorem Conservation of mechanical energy Lecture 11 Purdue University, Physics 220 7 Imagine that you are comparing three different ways of having...
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 Spring '09
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