14 - Work-Energy Theorem

14 - Work-Energy Theorem - Work Read 8.1-8.2 HW - Chapter 7...

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Work Read 8.1-8.2 HW - Chapter 7 Problems: 12, 16, 28
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How does the kinetic energy change? x F KE x F KE x F KE = 0
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Work Work =⋅ Fx parallel = cos = ∆θ F parallel F θ x Only the component of F along the direction of the displacement counts
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Dot (scalar) product A B xx xy xz yx yy yz zx z y zz AB AB AB +⋅+⋅ +⋅+⋅+⋅ ++ + = ii i j ik j i jj j k ki kj k AB k xyz A AA B BB =++ Aijk Bijk A == A A BA B 1 ⋅=⋅= ⋅ = ii jj kk 0 ⋅=⋅ = ⋅= ij jk ki
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Using the dot product xy FF =+ Fij ( ) ( ) 00 1000 cos37 1000 sin37 NN ij ( ) 5 m ∆= xi ( ) ( ) 0 1000 5 WN m =⋅ Fx x = 5m 37 o F = 1000 N 37 o F = 1000 N Same! 4000 J W =
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Tractor pull A tractor drags a 60 kg sled for a distance of 50 m. The drag rope makes an angle of 20 o with the ground and has a tension of 200 N. How much work does the tractor perform? How much work is done by gravity? The coefficient of kinetic friction is 0.3. How much work is done by friction?
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Tractor pull mg N f T θ ± m = 60 kg ± T = 200 N ± = 20 o ± x = 50 m ± µ k = 0.3
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Tractor pull cos tractor WF x =∆ θ () ( ) 200 N
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This note was uploaded on 04/13/2008 for the course PHYS 211 taught by Professor Shannon during the Spring '08 term at MSU Bozeman.

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14 - Work-Energy Theorem - Work Read 8.1-8.2 HW - Chapter 7...

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