# Lecture10 - PHYSICS 220 Lecture 10 Work and Kinetic Energy...

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Lecture 10 Purdue University, Physics 220 1 Lecture 10 Work and Kinetic Energy Textbook Sections 6.1 - 6.3 PHYSICS 220

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Lecture 10 Purdue University, Physics 220 2 Overview • Last Lecture – Non-Uniform Circular Motion – Kepler’s Laws • Today – Energy – Work
Lecture 10 Purdue University, Physics 220 3 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

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Lecture 10 Purdue University, Physics 220 4 Work and Energy θ • Work: Transfer of Energy by Force W F = |F| | Δ r| cos θ • Kinetic Energy (Energy of Motion) K = 1/2 mv 2 • Work-Kinetic Energy Theorem: Σ W = Δ K
Lecture 10 Purdue University, Physics 220 5 Work by Constant Force • Only component of force parallel to direction of motion does work! – W = F Δ r cos θ F θ Δ r F W F > 0: 0< θ < 90 : cos( θ ) > 0 Δ r F W F = 0: θ =90 : cos( θ ) =0 Δ r F W F < 0: 90< θ < 270 : cos( θ ) < 0 Δ r F W F > 0: 0< θ < 90 : cos( θ ) > 0

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Lecture 10 Purdue University, Physics 220 6 Quiz You toss a ball in the air. The work done by gravity as the ball goes up is: A) Positive B) Negative C) Zero
Purdue University, Physics 220 7 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

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## This note was uploaded on 09/17/2010 for the course PHYS 220 taught by Professor Chang during the Spring '09 term at Purdue University-West Lafayette.

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Lecture10 - PHYSICS 220 Lecture 10 Work and Kinetic Energy...

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