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Classical Mechanics Lecture 9 Today's Concepts and Examples: a) Energy and Friction b) Potential energy & force Mechanics Lecture 9, Slide 1 Midterm 2 will be held on March 13. Covers units 4-9 Unit 9 Homework Due Thursday March 12 11:30 PM. No extension!
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Homework 8. Awesome Job! Mechanics Lecture 8, Slide 2 Average = 92%
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Practice Exams Mechanics Lecture 8, Slide 3 Phys 1500 Exams https://utah.instructure.com/courses/320947/files - Spring 2013: http://www.physics.utah.edu/~springer/phys1500/exams/MidtermExam2.pdf http://www.physics.utah.edu/~springer/phys1500/exams/MidtermExam2.pdf - Solutions: http://www.physics.utah.edu/~springer/phys1500/exams/MidtermExam2Soln.pdf http://www.physics.utah.edu/~springer/phys1500/exams/MidtermExam2Soln.pdf - Long Sample: https://utah.instructure.com/courses/320947/files/45779670/download?wrap=1https://utah.instructure.com/courses/320947/files/45779670/download?wrap=1 Phys 2210 Exams - Practice : http://www.physics.utah.edu/~woolf/2210_Jui/rev2.pdfhttp://www.physics.utah.edu/~woolf/2210_Jui/rev2.pdf - Spring 2015: http://www.physics.utah.edu/~woolf/2210_Jui/ex2.pdfhttp://www.physics.utah.edu/~woolf/2210_Jui/ex2.pdf
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Main Points Mechanics Lecture 8, Slide 4
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Main Points Mechanics Lecture 8, Slide 5
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Incline with Friction: Work-Kinetic Energy Mechanics Lecture 8, Slide 6 Using Work-Kinetic Energy Theorem Same result as using Newton’s Law
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H N1N1 mg N2N2 mg must be negative m Work by Friction :W friction <0 Mechanics Lecture 9, Slide 7 What is the macroscopic work done on the block by friction during this process? A) mgH B) –mgH C) k mgD D) 0
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Checkpoint Mechanics Lecture 8, Slide 8 What is the total macroscopic work done on the block by all forces during this process? A) mgH B) –mgH C) k mgD D) 0 Mechanics Lecture 9, Slide 8 D m H
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Mechanics Lecture 8, Slide 9
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Force from Potential Energy:1D Mechanics Lecture 8, Slide 10
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Force from Potential Energy in 3-d Mechanics Lecture 8, Slide 11 Gradient operator
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Potential Energy vs. Force Mechanics Lecture 9, Slide 12
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Potential Energy vs. Force Mechanics Lecture 9, Slide 13
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Potential Energy vs. Force Mechanics Lecture 9, Slide 14
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Potential Energy vs. Force Mechanics Lecture 9, Slide 15
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Demo Potential Energy vs. Force Mechanics Lecture 9, Slide 16
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Equilibrium Mechanics Lecture 8, Slide 17
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Equilibrium points Mechanics Lecture 8, Slide 18
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Equilibrium points Mechanics Lecture 8, Slide 19
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Equilibrium points Mechanics Lecture 8, Slide 20
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Block on Incline Mechanics Lecture 8, Slide 21
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Block on Incline Mechanics Lecture 8, Slide 22
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Block on Incline Mechanics Lecture 8, Slide 23
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Block on Incline Mechanics Lecture 8, Slide 24
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Energy Conservation Problems in general Mechanics Lecture 8, Slide 25 For systems with only conservative forces acting E mechanical is a constant
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Gravitational Potential Energy Mechanics Lecture 8, Slide 26
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Gravitational Potential Problems Mechanics Lecture 8, Slide 27 conservation of mechanical energy can be used to “easily” solve problems. Define coordinates: where is U=0? as Add potential energy from each source.
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Trip to the moon Mechanics Lecture 8, Slide 28
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Trip to the moon Mechanics Lecture 8, Slide 29 Can ignore effect of moon for this problem at level of precision for SmartPhysics
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Trip to the moon Mechanics Lecture 8, Slide 30 …or you can practice solving the quadratic equation with many terms!!!
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Trip to the moon Mechanics Lecture 8, Slide 31 Can NOT ignore effect of moon for this problem since the rocket is AT the moon in the end !!!!
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Trip to the moon Mechanics Lecture 8, Slide 32
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Trip to the moon Mechanics Lecture 8, Slide 33
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Trip to the moon Mechanics Lecture 8, Slide 34 x x
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Block on Incline 2 Mechanics Lecture 8, Slide 35
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Block on Incline 2 Mechanics Lecture 8, Slide 36
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Block on Incline 2 Mechanics Lecture 8, Slide 37
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Block on Incline 2 Mechanics Lecture 8, Slide 38
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Clicker Question A. B. C. D. Mechanics Lecture 8, Slide 39 Suppose the potential energy of some object U as a function of x looks like the plot shown below. Where is the force on the object zero? A) (a) B) (b) C) (c)D) (d) U(x)U(x) x (a)(b) (c)(d)
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Clicker Question A. B. C. D. Mechanics Lecture 8, Slide 40 Suppose the potential energy of some object U as a function of x looks like the plot shown below. Where is the force on the object in the +x direction? A) To the left of (b) B) To the right of (b) C) Nowhere U(x)U(x) x (a)(b) (c)(d)
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Clicker Question A. B. C. D. Mechanics Lecture 8, Slide 41 Suppose the potential energy of some object U as a function of x looks like the plot shown below. Where is the force on the object biggest in the –x direction? A) (a) B) (b) C) (c)D) (d) U(x)U(x) x (a)(b) (c)(d)
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