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Lecture09_Pushkar_tentative

# Lecture09_Pushkar_tentative - PHYSICS 220 Lecture 9 Work...

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Lecture 9 Purdue University, Physics 220 1 Lecture 9 Work and Kinetic Energy PHYSICS 220

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Lecture 9 Purdue University, Physics 220 2 Energy Energy is “conserved” meaning it can not be created nor destroyed Can change form Can be transferred Total Energy of an isolated system does not change with time Types Kinetic Energy Potential Energy Rest Energy (E=mc 2 ) Thermal Energy … … Units: Joule (J) = N m = kg m 2 / s 2
Lecture 9 Purdue University, Physics 220 3 Work and Energy θ Work: Transfer of Energy by Force W = | F | | r | cos θ Kinetic Energy (Energy of Motion) KE = 1/2 mv 2 Work-Kinetic Energy Theorem: Σ W = KE

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Lecture 9 Purdue University, Physics 220 4 Work by Constant Force Only component of force parallel to direction of motion does work! W = F r cos θ F θ r F W F > 0: 0< θ < 90 : cos( θ ) > 0 r F W F = 0: θ =90 : cos( θ ) =0 r F W F < 0: 90< θ < 270 : cos( θ ) < 0 r F W F > 0: 0< θ < 90 : cos( θ ) > 0
Lecture 9 Purdue University, Physics 220 5 Work by Constant Force Example: You pull a 30 N chest 5 meters across the floor at a constant speed by applying a force of 50 N at an angle of 30 degrees. How much work is done by the 50 N force? 30 50 N W = T x cos θ = (50 Ν 29 (5 m ) cos (30) = 217 Joules T mg N f

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Lecture 9 Purdue University, Physics 220 6 Where did the Energy go?
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