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Lecture09_Pushkar_2011

# Lecture09_Pushkar_2011 - PHYSICS 220 Lecture 9 Work and...

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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 Newton’s Second Law leads to definitions of work and energy The connection between force and energy is work
Lecture 9 Purdue University, Physics 220 3 Work and Energy Work: Transfer of Energy by Force W = | F | | r | cos θ W depends on the direction of the force relative to the displacement

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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 iClicker You toss a ball in the air. The work done by gravity as the ball goes up is: A) Positive B) Negative C) Zero

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Lecture 9 Purdue University, Physics 220 6 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
Lecture 9 Purdue University, Physics 220 7 Question You are towing a car up a hill with constant velocity . The work done on the car by the normal force is: A) positive B) negative C) zero T W N V Normal force is perpendicular to direction of displacement,  so work is zero.

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Lecture 9 Purdue University, Physics 220 8 You are towing a car up a hill with constant velocity .
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Lecture09_Pushkar_2011 - PHYSICS 220 Lecture 9 Work and...

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