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Phys 141_HW Sol_Ch11_W08

# Phys 141_HW Sol_Ch11_W08 - Cal Poly State University SLO...

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Cal Poly State University, SLO D. Niebuhr Physics Department Winter 2008 Phys 141 Homework Solutions Chapter 11 Assigned Problems: Ch. 11: 2, 6, 14, 16, 23, 28, 34, 45, 48, 54, 60, 53 11.2. Visualize: Please refer to Figure Ex11.2. Solve: (a) cos (3)(4)cos110 4.1. A B AB α = = ° = - r r (b) cos (4)(5)cos180 20. C D CD = = ° = - r r (c) cos (4)(3)cos30 10.4. E F EF = = ° = r r 11.6. Solve: (a) y ¡º ª * ( 5.0 4.0 ) N (3.0 ) m ( 15.0 12.0 ) J= 15.0 J. W F r i j i i i j i = ⋅∆ = - + = - ⋅ + - r r r (b) y ¡ ≡♠ ( 5.0 4.0 ) N ( 3.0 ) m (15.0 12.0 ) J= 12.0 J. W F r i j j i j j j = ⋅∆ = - + ⋅ - = ⋅ - - r r r 11.14. Model: Use the work-kinetic energy theorem. Visualize: Please refer to Figure Ex11.14. Solve: The work-kinetc energy theorem is f i f x 2 2 f i i f x 2 2 2 f f 0 m 1 1 area under the force curve from to 2 2 1 1 1 (2 kg)(4.0 m/s) 16 J area from 0 to 2 2 2 x x x K mv mv W F dx x x mv mv F dx x = - = = = - = - = = 2 f f 2 f f 1 1 At 2 m : (2.0 kg) 16 J ( 10 N)(2 m) 10 J 2.45 m/s 2 2 1 At 4 m : (2.0 kg) 16 J 0 J 4.0 m/s 2 x v v x v v = - = - = - = = - = = 11.16. Model: Use the definition / . s F dU ds = - Visualize: Please refer to Figure Ex11.16. Solve: F x is the negative of the slope of the potential energy graph at position x . Between x = 0 cm and x = 10 cm the slope is slope = f i f i ( )/( ) (0 J 10 J)/(0.1 m 0.0 m) 100 N U U x x - - = - - = - Thus, F x = 100 N at x = 5 cm. The slope between x = 10 cm and x = 20 cm is zero, so F x = 0 N at x = 15 cm. Between 20 cm and 40 cm, slope = (10 J 0 J)/(0.40 m 0.20 m) 50 N - - = At x = 25 cm and x = 35 cm, therefore, F x = - 50 N.

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Cal Poly State University, SLO D. Niebuhr Physics Department Winter 2008 Phys 141 11.23. Visualize: Solve: (a) 2 2 i 0 0 i g0 0 2 2 ext f 1 1 f g1 1 1 0 J (20 kg)(9.8 m/s )(3 m) 588 J 2 1 1 0 J (20 kg)(2.0 m/s) 40 J 0 J 2 2 K K mv U U mgy W K K mv U U mgy = = = = = = = = = = = = = = = At the top of the slide, the child has gravitational potential energy of 588 J. This energy is transformed into thermal energy of the child’s pants and the slide and the kinetic energy of the child. This energy transfer and transformation is shown on the energy bar chart. (b)
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Phys 141_HW Sol_Ch11_W08 - Cal Poly State University SLO...

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