Lecture_9

Lecture_9 - REVIEW of Last Weeks Lecture B B cos Scalar Product A A B AB cos Ax Bx Ay B y Az Bz Work W Fs constant force parallel to displacement W

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P123 Lecture 9 29 October 2010 Power and Gravitational Potential Energy REVIEW of Last Week’s Lecture Scalar Product A B cos B Work z z y y x x B A B A B A AB B A cos constant force parallel to displacement F W constant not parallel to variable force along x (area under F-x curve) F s 2 2 1 dx F W s F W Fs x x x Work-Energy Theorem 2 in general 1 s d F W Kinetic Energy 1 2 1 K K K s d F W net tot 2 2 1 ; Where MV K F F r i net Spring, Hooke’s Law kx F x 1 displacement from equilibrium 2 2 1 kx W
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i Clicker cow A piece of fruit falls straight down. As it falls, the gravitational force: F s cow s F W A. Does positive work B. Does negative work C. Does no work D. First does negative work, then positive work E. First does positive work, then negative work
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POWER Rate at which work is done t W P AV (Rate at which energy changes) dt dW t W P t 0 lim Units: 1 Watt = 1 Joule/sec 1 Joule = 1 WS (Light bulb ~ 100W) (Numans ~ 100W) (1 hp = 746W) EXAMPLE: A 5 kg mass falls 3.2 meters. What is the average power generated by gravity? 2 s 0.8 s 64 . 0 ) m/s 10 ( ) m 2 . 3 ( 2 2 2 2 2 1 g s t gt s J 160 ) m 2 . 3 )( m/s 10 )( kg 5 ( s mg s F W W 200 ) s 8 . 0 ( ) J 160 ( AV P The can stops the mass in 1/10 the time it takes to fall.
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This note was uploaded on 03/14/2011 for the course P 123 taught by Professor Stevens during the Spring '11 term at Rust.

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Lecture_9 - REVIEW of Last Weeks Lecture B B cos Scalar Product A A B AB cos Ax Bx Ay B y Az Bz Work W Fs constant force parallel to displacement W

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