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Conservation of Energy Energy1 = Energy2 + Friction
Chapter Conservation of Energy Energy1 = Energy2 + Friction
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Objectives Establish a standard energy equation
Establish initial and final conditions Solve for unknown variable
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Types of Energy Work Spring Work Potential Energy Kinetic Energy
Friction Work U = (F) x (s) SP = (½)kx2 PE = W x h KE = (½)mv2 Fr = Ff x (s)
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Conservation of Energy
Energy at condition (1) equals Energy at condition (2) plus friction KE1+PE1+SP1=KE2+PE2+SP2+Fr (½)mv12 +Wh1+(½)kx12 = (½)mv22 +Wh2+(½)kx22 + Ff (x)
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Example 14 – 10 Conditions: v1=20 ft/s v2 = 0 ft/s
h1 = 0 ft h2 = d(sin 30) No spring component Friction = 5 lbs
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Example 14 – 10 Solution (½)(W/g)v12 +Wh1+(½)kx12 =
(½))(W/g) v22 +Wh2+(½)kx22 + Ff(x) (Remove factors that equal zero) (½)(W/g)v12 =Wh2+Ff(x) (Substitute values) (.5)(100/32.2)(20)2=(100)(d)(.5)+(5)(d)
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Example 14 – 10 Answer (.5)(100/32.2)(20)2=(100)(d)(.5)+(5)(d)
d=11.3 ft
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Angular Kinetic Energy
Rectilinear KE = (½)mv2 Angular KE = (½)I2 Where: KE in ft-lbs or n-m I in ft-lb-s2 or kg-m2 in rad/sec
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Week 12 Homework Chapter 14 Problems: 26, 27, 35, 37, 43, 50 & 59 (7th Ed) Problems: 29, 30, 38, 40, 46, 53 & 62 (8th Ed) Read Sections thru for next week
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