WorkEnergy

# WorkEnergy - Physics 201: Lecture 10 Work &amp; Energy...

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3/27/08 Physics 201, UW-Madison 1 Physics 201: Lecture Physics 201: Lecture 10 10 Definition Work done by a constant force Work/kinetic energy theorem Work done by multiple constant forces

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3/27/08 Physics 201, UW-Madison 2 Definition of Work: Definition of Work: Ingredients: Ingredients: Force ( F ), displacement ( Δ r ) Work, W , of a constant force F acting through a displacement Δ r is: θ F Δ r displacement F r Vector “Dot Product” W = ! F i ! ! r = F ! r cos " = F r ! r
3/27/08 Physics 201, UW-Madison 3 Definition of Work. .. Definition of Work. .. Only the component of F along the displacement is doing work. Example: Train on a track. If you push on it at θ =90 o the train does not move; no work is done. F Δ r θ F cos θ

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3/27/08 Physics 201, UW-Madison 4 Question Question You lift an object 1 m from the floor to a shelf. The work done by the earths gravitational field on the object is: Positive No work is done Negative InsufFcient information
3/27/08 Physics 201, UW-Madison 5 Question Question You push a heavy box 1 m across a rough floor. Which statements are correct? You have done positive work on the box. You have done negative work on the box. The earths gravitational feld has done negative work on the box The normal Force has done positive work on the box You have done negative work on the outside world

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3/27/08 Physics 201, UW-Madison 6 Back to the definition of Work: Back to the definition of Work: Total Work, W , of a force F acting through a displacement Δ x is: F x x W = F x ! x ( ) i i " Δ x i F i W tot = F x dx x 1 x 2 ! Work = Area under F(x) curve
Physics 201, UW-Madison 7 Problem Problem 1: 1: A box is pulled up a rough ( μ > 0 ) incline by a rope-pulley- weight arrangement as shown below. How many forces are doing work on the box?

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## This note was uploaded on 03/27/2008 for the course PHYS 201 taught by Professor Walker during the Spring '08 term at Wisconsin.

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WorkEnergy - Physics 201: Lecture 10 Work &amp; Energy...

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