# L9F11 - P123F11 REVIEW of Last Weeks Lecture Scalar Product...

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1 P123 F11 Lecture 9 28 October 2011 Power and Gravitational Potential Energy REVIEW of Last Week’s Lecture Scalar Product Work Work-Energy Theorem Spring, Hooke’s Law displacement from equilibrium 2 2 1 kx W kx F x z z y y x x B A B A B A AB B A cos Kinetic Energy 1 2 2 1 K K K s d F W net tot 2 2 1 ; Where MV K F F r i net constant force parallel to displacement constant not parallel to variable force along x (area under F-x curve) in general F s 2 1 2 1 s d F W dx F W s F W Fs W x x x A B cos B

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A piece of fruit falls straight down. As it falls, the gravitational force: 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 i Clicker F s s F W cow cow
3 t W P AV dt dW t W P t 0 lim s 0.8 s 64 . 0 ) m/s 10 ( ) m 2 . 3 ( 2 2 2 2 2 1 g s t gt s W 200 ) s 8 . 0 ( ) J 160 ( AV P EXAMPLE: A 5 kg mass falls 3.2 meters. What is the average power generated by gravity? The can stops the mass in 1/10 the time it takes to fall. How much power is supplied by the can?

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L9F11 - P123F11 REVIEW of Last Weeks Lecture Scalar Product...

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