Discussion08 - – 1 gallon of gas/hour ≈ 39,000 W – 1...

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Work and General Physics I Mechanics Racquetball Striking a Wall Kinetic Energy Physics 140 Mt. Etna Stewart Hall
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Work and Kinetic Energy • Constant force and straight-line displacement: • Varying force or curved trajectory: F s φ z F y F x F Fs s F Fs s F W z y x + + = = = = = || || cos ϕ r r = = ds F s d F W cos r r • One dimensional motion, position dependent force: • Kinetic energy: • Work-energy theorem: + + = dz F dy F dx F W z y x = 2 1 ) ( x x x dx x F W - area under the curve F x (x) 2 / 2 mv KE = f tot i KE W KE = +
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Power Power is the rate at which work is done: • The SI unit of power is Watt: 1 W = 1 J/s • In the case of a constant force dt dW P = ( 29 v F t s d F s F t d t dW P r r r r r r = = = = • Power is something we encounter all the time, because energy is something we pay for. A couple of simple conversions:
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Unformatted text preview: – 1 gallon of gas/hour ≈ 39,000 W – 1 light bulb ≈ 100 W • So if you want to save energy, don’t bother to turn off the lights – just drive less instead dt dt dt Question 6.24 A. ½ W B. W C. 2 W D. 3 W E. 4 W Question 6.24 A. ½ W B. W C. 2 W D. 3 W E. 4 W Problem 6.20 Problem 6.34 (c): A. 20 J B. 40 J C. 60 J D. 80 J E. 120 J Problem 6.34 (c): A. 20 J B. 40 J C. 60 J D. 80 J E. 120 J Problem 6.86 Problem 6.98 Problem 6.52 Example • An object of mass m is moving along the positive x-axis, and at x = 0 its velocity is v • A force F = -ax 3 i acts on the object, where a is a positive constant t what position long the xis will the • At what position x along the x-axis will the object’s speed be v /2?...
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This note was uploaded on 02/15/2012 for the course PHYS 140 taught by Professor Uher during the Winter '10 term at University of Michigan.

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Discussion08 - – 1 gallon of gas/hour ≈ 39,000 W – 1...

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