lecture22[1] - Potential Energy Conservative and...

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1 Physics 1D03 - Lecture 22 Potential Energy Serway 7.6, 7.7; 8.1 – 8.2 Conservative and non-conservative forces Gravitational and elastic potential energy Mechanical Energy Practice problems: Serway chapter 7, problems 41, 43 chapter 8, problems 5, 11, 43, 53 Physics 1D03 Potential energy -another approach to calculating the work done -only possible for “conservative” forces -leads to the idea of energy as a conserved quantity The basic idea: Work done by a force is equal to the decrease in potential energy: Work = - (change in potential energy)
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2 Physics 1D03 Example: Gravitational Work s 2 y s 1 m g When the block is lowered, gravity does work: W g1 = m g . s 1 = mgy or W g2 = m g . s 2 = mgy y m g F P = m g To lift the block to a height y requires work (by F P :) W P = mgy Physics 1D03 Work done (against gravity) to lift the box is “stored” as gravitational potential energy U g : U g =(weight) x (height) = mgy (uniform g ) When the block moves, (work by gravity) = P.E. lost
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lecture22[1] - Potential Energy Conservative and...

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