Lect05

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Unformatted text preview: W F dr F dr F dr F dr 9 r2 r1 F dr ! "# WTOT K>0 K W>0 or W<0 ! "# $ $ K<0 W=0 K=0 & ' ' $ + ' $ " ( ( * " + + ) F Coulomb force does negative work Potential energy increases % x + + Analogy to gravity m Exert force Fext = - Fg over distance h. Fext m h Fg Work by me = Fext h = - Fgh = mgh = U h 0 Fext d r h 0 Fg d r Ug h Ug 0 Ug Work by me - (Work by gravity) Change in Potential energy ( , A charge is released from rest in a region of electric field. The charge will start to move A) in a direction that makes its potential energy increase B) in a direction that makes its potential energy decrease C) along a path of constant potential energy F x It will move in the same direction as F Work done by force is positive U = -Work is negative Nature wants things to move in such a way that PE decreases 34 7 6 ' FE " 7 $ ( FH 8 $ + E ./...
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This document was uploaded on 03/08/2012.

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