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Lecture10_Pushkar - PHYSICS 220 Lecture 10 Potential Energy...

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Lecture 10 Purdue University, Physics 220 1 Lecture 10 Potential Energy and Energy Conservation PHYSICS 220
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Lecture 10 Purdue University, Physics 220 2 Potential Energy Work done by gravity is independent of path W g = -mg (y f - y i ) = - PE g • Define PE 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
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Lecture 10 Purdue University, Physics 220 3 Work by Variable Force W = F x x Work is the area under the F vs x plot -W= PE s = 1/2 k x 2 Spring: F spring = -k x Potential Energy:
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Lecture 10 Purdue University, Physics 220 4 Work-Energy with Conservative Forces W nc = ∆ K E + PE Move work by conservative forces to other side If there are NO non-conservative forces 0 = ∆ KE + PE = ∆ E mech 0 = KE f - KE i + PE f - PE i KE i + PE i = KE f + PE f Work-Energy Theorem W = ∆ K E Conservation of mechanical energy E i = E f Σ W = W cons + W nc = ∆ KE W nc =∆ KE - W cons
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Lecture 10 Purdue University, Physics 220 5 Imagine that you are comparing three different ways of having a ball move down through the same height. In which case does the ball reach the bottom with the highest speed? A) Dropping B) Slide on ramp (no friction) C) Swinging down D) All the same A B C Conservation of Energy (W nc =0) KE initial + PE initial = KE final + PE final 0 + mgh = ½ m v 2 final + 0 v final = sqrt(2 g h) iClicker correct
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This note was uploaded on 02/21/2010 for the course PHYS 220 taught by Professor Chang during the Spring '09 term at Purdue.

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Lecture10_Pushkar - PHYSICS 220 Lecture 10 Potential Energy...

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