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# L26 - Remember:This/NextWeek ReadCh.6&Ch.7:Ch.7.17.6,7.8...

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Remember: This/Next Week Read Ch. 6 & Ch. 7: Ch. 7.1 – 7.6, 7.8. CAPA assignment #9 is due this evening at 10 PM, to be done on‐line. Recitation next week: Required! Recitation is a Review of Chs. 1-7. Print & bring to Lab. Make-Up Lab Period: Let your TA know. Problem session: Monday, Place: TBD. L26 F 3/13/09 1 Physics 2010

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CH. 6: Extra QuesPons & problems Questions: 7, 10, 11, 17, 22, 24. Problems: Work: 5, 6 Kinetic Energy: 18, 21 Potential Energy: 27, 29, 32 Conservation of Mech. Energy: 35, 37, 41, 43 Conservation of Energy: 50, 52, 54 Power: 60, 66 L26 F 3/13/09 2 physics 2010
L26 F 3/13/09 Physics 2010 3 General Statement of Conservation of Energy Δ E mechanical + Δ E thermal = W external E mechanical = KE + PE Δ E thermal = thermal energy generated = -W frict W external = external work done on the system (work done by sliding friction) KE i + PE i + W frict + W external = KE f + PE f PE grav = mgy PE elastic = ½ kx 2

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L25 W 3/10/10 Physics 2010 4 Springs, Hooke’s “Law”, and Elastic Potential Energy F = -kx Hooke’s “Law” k = “spring constant” Units = N/m x = displacement - sign = spring resists stretching Large k = stiff spring Small k = ±oppy spring
L25 W 3/10/10 Physics 2010 5 Springs, Hooke’s “Law”, and Elastic Potential Energy F = -kx Hooke’s “Law” Elastic potential energy: PE = ½ kx 2 Δ PE = W ext = F avg x = ½ kx 2 Compress spring by amount x: F avg = ½ kx.

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L25 W 3/10/10 Physics 2010 6 F = -kx, PE =1/2 kx 2 A force of magnitude F stretches a spring through a displacement x. Force is then increased so that displacement is doubled. What is the magnitude of force needed to double the displacement and what will be the effect on the potential energy of doubling displacement?
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L26 - Remember:This/NextWeek ReadCh.6&Ch.7:Ch.7.17.6,7.8...

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