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sy07_sept26_07hc

# sy07_sept26_07hc - Physics 207 Lecture 7 Physics 207...

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Page 1 Physics 207 – Lecture 7 Physics 207: Lecture 7, Pg 1 Physics 207, Physics 207, Lecture 7, Sept. 26 Lecture 7, Sept. 26 Agenda: Assignment: For Wednesday read Chapter 7 Assignment: For Wednesday read Chapter 7 circle6 MP Problem Set 3 due tonight MP Problem Set 3 due tonight circle6 MP Problem Set 4 available now MP Problem Set 4 available now circle6 MidTerm MidTerm Thursday, Oct. 4, Chapters 1 Thursday, Oct. 4, Chapters 1- 7, 90 minutes, 7:15 7, 90 minutes, 7:15- 8:45 PM 8:45 PM Rooms: B102 & B130 in Van Vleck . Chapter 6 (Dynamics II) xrhombus Motion in two (or three dimensions) xrhombus Frames of reference Start Chapter 7 (Dynamics III) xrhombus Circular Motion Physics 207: Lecture 7, Pg 2 Chapter 6: Chapter 6: Motion in 2 (and 3) dimensions Motion in 2 (and 3) dimensions , Dynamics II Dynamics II circle6 Recall instantaneous velocity and acceleration circle6 These are vector expressions reflecting x, y and z motion r = r (t) v = d r / dt a = d 2 r / dt 2 Physics 207: Lecture 7, Pg 3 Kinematics circle6 The position, velocity, and acceleration of a particle in 3-dimensions can be expressed as: r = x i + y j + z k v = v x i + v y j + v z k ( i , j , k unit vectors ) a = a x i + a y j + a z k circle6 All this complexity is hidden away in this compact notation r = r (t) v = d r / dt a = d 2 r / dt 2 a d x dt x = 2 2 a d y dt y = 2 2 a d z dt z = 2 2 v dx dt x = v dy dt y = v dz dt z = ) ( t x x = y y t = ( ) z z t = ( ) Physics 207: Lecture 7, Pg 4 Special Case Special Case Throwing an object with x along the horizontal and y along the vertical. x and y motion both coexist and t is common to both Let g act in the y direction, v 0x = v 0 and v 0y = 0 y t 0 4 x t = 0 4 y t x 0 4 x vs t y vs t x vs y Physics 207: Lecture 7, Pg 5 A different trajectory A different trajectory x vs y t = 0 t =10 Can you identify the dynamics in this picture? How many distinct regimes are there? y x Physics 207: Lecture 7, Pg 6 A different trajectory x vs y t = 0 t =10 Can you identify the dynamics in this picture? How many distinct regimes are there? 0 < t < 3 3 < t < 7 7 < t < 10 barb4left I. v x = constant = v 0 ; v y = 0 barb4left II. v x = v y = v 0 barb4left III. v x = 0 ; v y = constant < v 0 y x What can you say about the acceleration?

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Page 2 Physics 207 – Lecture 7 Physics 207: Lecture 7, Pg 7 Lecture 7, Exercises 1 & 2 Trajectories with acceleration circle6 A rocket is moving sideways in deep space, with its engine off, from A to B. It is not near any stars or planets or other outside forces. circle6 Its constant thrust engine (force is constant) is fired at point B and left on for 2 seconds in which time the rocket travels from point B to some point C xrhombus Sketch the shape of the path from B to C. circle6 At point C the engine is turned off. xrhombus Sketch the shape of the path after point C Physics 207: Lecture 7, Pg 8 Lecture 7, Exercise 1 Trajectories with acceleration A. A B. B C. C D. D E.
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