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Unformatted text preview: KE + PE. Work Done by a Variable Force
The work W done by N variable forces F1, F2,..., FN through displacements s1, s2, ..., sN is given by
W ( F cos ) s + ( F cos ) s + + ( FN cos N ) s N = N i= ( Fi cos i ) si where i is the angle between the force Fi and displacement si. Geometric Meaning of the Work Done by a Variable Force
Force Displacement Two Types of Forces A conservative force is a force acting on a
body that obeys the conservation of energy principle. For example, the force of gravity acting on a body. Any force that acts on an body so that the total energy before is not equal to the total energy after is called a nonconservative force. For example, friction, air resistance or a propulsion force acting on a body. NonConservative Forces & Work
The work Wnc done by nonconservative forces is given by either Wnc = KE + PE or = ( KE after  KE before ) + ( PE after  PEbefore ) Wnc = Eafter  Ebefore = = ( KEafter + PEafter )  ( KEbefore + PEbefore ) . Another Form of NonConservative Work
Another form of the nonconservative work Wnc done by external forces is given by KEafter + PEafter + Energy Output = = KEbefore + PEbefore + Energy Input Average Power
The average power P is the rate at which energy is transferred to or from a body over a given time interval t. W P= t
The SI unit of power is the Watt=J/s....
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This note was uploaded on 02/10/2010 for the course PHY 2053 taught by Professor Hardy during the Spring '10 term at University of Southern Maine.
 Spring '10
 Hardy
 Physics, Conservation Of Energy, Energy, Force, Power, Work

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