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9/24/2013PHY 113 C Fall 2013-- Lecture 91 PHY 113 C General Physics I 11 AM-12:15 PM MWF Olin 101 Plan for Lecture 9: 1.Review (Chapters 1-8) 2.Exam preparation.

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Presentation on theme: "9/24/2013PHY 113 C Fall 2013-- Lecture 91 PHY 113 C General Physics I 11 AM-12:15 PM MWF Olin 101 Plan for Lecture 9: 1.Review (Chapters 1-8) 2.Exam preparation."— Presentation transcript:

1 9/24/2013PHY 113 C Fall Lecture 91 PHY 113 C General Physics I 11 AM-12:15 PM MWF Olin 101 Plan for Lecture 9: 1.Review (Chapters 1-8) 2.Exam preparation advice – 3.Example problems

2 9/24/2013 PHY 113 C Fall Lecture 92

3 9/24/2013PHY 113 C Fall Lecture 93 iclicker question What is the best way to prepare for Thursday’s exam? A.Read Lecture Notes and also reread Chapters 1- 8 in Serway and Jewett.Lecture Notes B.Prepare equation sheet. C.Solve problems from previous exams. D.Solve homework assignments (both graded and ungraded) from Webassign Assignments 1-8 E.All the above

4 9/24/2013PHY 113 C Fall Lecture 94 iclicker question Have you (yet) accessed the online class lecture notes from previous classes? A.yes B.no iclicker question Have you (yet) accessed the passed Webassign Assignments (with or without the answer key)? A.yes B.no

5 9/24/2013PHY 113 C Fall Lecture 95 Access to previous exams

6 9/24/2013PHY 113 C Fall Lecture 96 Previous exam access -- continued Overlap with 2013 schedule

7 9/24/2013PHY 113 C Fall Lecture 97 Comments on preparation for next Thursday’s exam – continued What you should bring to the exam (in addition to your well-rested brain):  A pencil or pen  Your calculator  An 8.5”x11” sheet of paper with your favorite equations (to be turned in together with the exam) What you should NOT use during the exam  Electronic devices (cell phone, laptop, etc.)  Your textbook

8 Advice: 1.Keep basic concepts and equations at the top of your head. 2.Practice problem solving and math skills 3.Develop an equation sheet that you can consult. Equation Sheet Problem solving skills Math skills 9/24/2013PHY 113 C Fall Lecture 98

9 9/24/2013PHY 113 C Fall Lecture 99 iclicker exercise Does the previous slide annoy you? A.yes B.no

10 Problem solving steps 1.Visualize problem – labeling variables 2.Determine which basic physical principle(s) apply 3.Write down the appropriate equations using the variables defined in step 1. 4.Check whether you have the correct amount of information to solve the problem (same number of knowns and unknowns). 5.Solve the equations. 6.Check whether your answer makes sense (units, order of magnitude, etc.). 9/24/2013PHY 113 C Fall Lecture 910

11 9/24/2013PHY 113 C Fall Lecture 911 Likely exam format (example from previous exam)

12 9/24/2013PHY 113 C Fall Lecture 912 Likely exam format (example from previous exam)

13 9/24/2013PHY 113 C Fall Lecture 913 Review of slides from previous lectures

14 9/24/2013PHY 113 C Fall Lecture 914 Mathematics Review -- Appendix B Serwey & Jewett a b c 

15 9/24/2013PHY 113 C Fall Lecture 915 One dimensional motion -- Summary of relationships

16 9/24/2013PHY 113 C Fall Lecture 916 Special relationships between t,x,v,a for constant a:

17 9/24/2013PHY 113 C Fall Lecture 917 Vector addition: a b a – b Vector subtraction: a -b a + b Introduction of vectors

18 9/24/2013PHY 113 C Fall Lecture 918 axax ayay byby bxbx Treatment of vectors in component form

19 9/24/2013PHY 113 C Fall Lecture 919 Vectors relevant to motion in two dimenstions Displacement: r(t) = x(t) i + y(t) j Velocity: v(t) = v x (t) i + v y (t) j Acceleration: a(t) = a x (t) i + a y (t) j

20 9/24/2013PHY 113 C Fall Lecture 920 Visualization of the position vector r(t) of a particle r(t 1 ) r(t 2 )

21 9/24/2013PHY 113 C Fall Lecture 921 Visualization of the velocity vector v(t) of a particle r(t 1 ) r(t 2 ) v(t)

22 9/24/2013PHY 113 C Fall Lecture 922 Visualization of the acceleration vector a(t) of a particle r(t 1 ) r(t 2 ) v(t 1 ) v(t 2 ) a(t 1 )

23 9/24/2013PHY 113 C Fall Lecture 923 Projectile motion (near earth’s surface) i j vertical direction (up) horizontal direction g = 9.8 m/s 2

24 9/24/2013PHY 113 C Fall Lecture 924 Projectile motion (near earth’s surface)

25 9/24/2013PHY 113 C Fall Lecture 925 Projectile motion (near earth’s surface) Trajectory equation in vector form: Aside: The equations for position and velocity written in this way are call “parametric” equations. They are related to each other through the time parameter. Trajectory equation in component form:

26 9/24/2013PHY 113 C Fall Lecture 926 Diagram of various trajectories reaching the same height h=1 m: y x 

27 9/24/2013PHY 113 C Fall Lecture 927 Projectile motion (near earth’s surface) Trajectory path y(x); eliminating t from the equations: Trajectory equation in component form:

28 9/24/2013PHY 113 C Fall Lecture 928 Isaac Newton, English physicist and mathematician (1642—1727) 1.In the absence of a net force, an object remains at constant velocity or at rest. 2.In the presence of a net force F, the motion of an object of mass m is described by the form F=ma. 3.F 12 =– F 21.

29 9/24/2013PHY 113 C Fall Lecture 929 Newton’s second law F = m a Types of forces: Fundamental Approximate Empirical Gravitational F=-mg j Friction Electrical Support Magnetic Elastic Elementary particles

30 9/24/2013PHY 113 C Fall Lecture 930 Example of two dimensional motion on a frictionless horizontal surface m

31 9/24/2013PHY 113 C Fall Lecture 931 Example – support forces  F support acts in direction  to surface (in direction of surface “normal”)

32 9/24/2013PHY 113 C Fall Lecture 932 Example of forces in equilibrium

33 9/24/2013PHY 113 C Fall Lecture 933 Example: 2-dimensional forces A car of mass m is on an icy (frictionless) driveway, inclined at an angle t as shown. Determine its acceleration. Conveniently tilted coordinate system:

34 9/24/2013 PHY 113 C Fall Lecture 934 vivi v f =0 Another example: Note: we are using a tilted coordinate frame i mg mg sin 

35 9/24/2013PHY 113 C Fall Lecture 935 Friction forces The term “friction” is used to describe the category of forces that oppose motion. One example is surface friction which acts on two touching solid objects. Another example is air friction. There are several reasonable models to quantify these phenomena. Surface friction: Material-dependent coefficient Normal force between surfaces Air friction: K and K’ are materials and shape dependent constants

36 9/24/2013PHY 113 C Fall Lecture 936 Models of surface friction forces (applied force) surface friction force f s,max =  s n Coefficients  s,  k depend on the surfaces; usually,  s >  k

37 9/24/2013PHY 113 C Fall Lecture 937 mg f n  mg sin  mg cos  Consider a stationary block on an incline: 

38 9/24/2013PHY 113 C Fall Lecture 938 V (constant)  mg n f=  k n Consider a block sliding down an inclined surface; constant velocity case

39 9/24/2013PHY 113 C Fall Lecture 939 mg f n  mg sin  mg cos  Summary 

40 9/24/2013PHY 113 C Fall Lecture 940 Uniform circular motion and Newton’s second law r

41 9/24/2013PHY 113 C Fall Lecture 941 Definition of work: F drdr riri rjrj

42 9/24/2013PHY 113 C Fall Lecture 942 Example:

43 9/24/2013PHY 113 C Fall Lecture 943 Work and potential energy Note: It is assumed that F is conservative

44 9/24/2013PHY 113 C Fall Lecture 944 Review of energy concepts:

45 9/24/2013PHY 113 C Fall Lecture 945 Summary of work, potential energy, kinetic energy relationships

46 9/24/2013PHY 113 C Fall Lecture 946 Example problem from Webassign #8 A baseball outfielder throws a kg baseball at a speed of 37.2 m/s and an initial angle of 31.0°. What is the kinetic energy of the baseball at the highest point of its trajectory? vivi ii yfyf vfvf

47 9/24/2013PHY 113 C Fall Lecture 947 Example problem from Webassign #8 The coefficient of friction between the block of mass m 1 = 3.00 kg and the surface in the figure below is μ k = The system starts from rest. What is the speed of the ball of mass m 2 = 5.00 kg when it has fallen a distance h = 1.85 m? h h f

48 9/24/2013PHY 113 C Fall Lecture 948 Example problem from Webassign #8 A block of mass m = 3.40 kg is released from rest from point A and slides on the frictionless track shown in the figure below. (Let h a = 6.70 m.).

49 9/24/2013PHY 113 C Fall Lecture 949 Example problem from 2012 Exam #2:

50 9/24/2013PHY 113 C Fall Lecture 950 Example problem from Webassign #5


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