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Accelerated Motion

Accelerated Motion. Chapter 3 Physics Principles and Problems Zitzewitz, Elliot, Haase, Harper, Herzog, Nelson, Nelson, Schuler and Zorn McGraw Hill, 2005. Acceleration - rate of change in velocity per unit time. http://www.free-computer-wallpapers.com/pictures/

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Accelerated Motion

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  1. Accelerated Motion Chapter 3 Physics Principles and Problems Zitzewitz, Elliot, Haase, Harper, Herzog, Nelson, Nelson, Schuler and Zorn McGraw Hill, 2005

  2. Acceleration - rate of change in velocity per unit time. http://www.free-computer-wallpapers.com/pictures/ albums/Car_wallpaper/Nascar_ea_sports500.jpg http://www.munciefreepress.com/files/images /October%202007%20%20Space%20Shuttle %20Discovery%20Launch%20-%201.preview.jpg

  3. Acceleration = ∆v / ∆t (vf - vi / tf - ti) • 8m/s - 4m/s = 4m/s = 2m/s2 4s - 2s 2s • Acceleration’s units are distance per time squared • What is the graph of an object that is decelerating? • What is the graph of an object at constant acceleration?

  4. Remember a distance vs time graph of an object that is accelerating is quadratic. • The rate of velocity is not constant. Since the velocity is changing per unit time so to is the distance traveled. • What is the distance-time graph of an object that is decelerating? http://www.gravitywarpdrive.com/ General_Relativity_Images/ Falling_Ball_Graph_Distance.gif

  5. Using the graph explain the acceleration and position of these 5 runners (assume east is positive). east A B v e l o c i t y (m/s) C D time (s) E west The sign of acceleration does not indicate whether or not The object is speeding up or slowing down (only its direction).

  6. Final Velocity with Average Acceleration a = ∆v OR ∆v = a ∆t OR vf - vi = a ∆t ∆t vf = vi + a ∆t Example 1: A bus that is traveling at 30.0km/hr speeds up at a constant rate of 3.5m/s2. What velocity does it reach 6.8s later? Example 2: A car slows from 22m/s to 3.0m/s at a constant rate of 2.1m/s2. How many seconds are required before the car is traveling at 3.0m/s?

  7. Position with Average Accelerationdf = di + vitf + 1/2atf2Velocity with Constant Accelerationvf2 = vi2 + 2a(df - di) • Example 1: Sekazi is learning to ride a bike. His father pushes him with a constant acceleration of 0.50m/s2 for 6.0s, and then Sekazi continues at 3.0m/s for 6.0s before falling. What is Sekazi’s displacement? • Example 2: Sunee is training for an upcoming 5.0km race. She starts out her training run by moving at a constant pace of 4.3m/s for 19min. Then she accelerates at a constant rate until she crosses the finish line 19.4s later. What is her acceleration during the last portion of the training run?

  8. Free Fall - the motion of an object due to the force of gravity (air resistance = 0). • Neglecting air resistance, all objects in free fall have the same acceleration. • Earth: g (acceleration due to gravity) = 9.8m/s2 • Sun: g = 275m/s2 • Venus: g = 8.9m/s2 • Moon: g = 1.6m/s2 • Jupiter: = 25m/s2 http://imagecache2.allposters.com/images/pic/EUR/2300-2025~Skydiving-Free-Fall-Formation-Posters.jpg http://www.robhainey.com/Made%20up%20signs/Constuction%20site/Warning%20falling%20objects%20400%20x%20300.jpg

  9. This same acceleration constant (9.8m/s2) applies to objects falling towards earth or moving away from earth. • When solving for free fall these same equations apply: • vf = vi + atf • df = di + vitf + 1/2at2 • vf2 = vi2 + 2a(df - di) http://ww1.prweb.com/prfiles/2006/10/04/0000446911/spudwebb.jpg http://www.onlinephys.com/freefall1.jpg

  10. Examples • You toss a ball up in the air at 35m/s. What is the velocity of the ball after 2.2s? 4.4s? 7.0s? • A construction worker accidentally drops a brick for a high scaffold. What is the velocity of the brick after 4.0s? How high was the scaffold? • A tennis ball is thrown straight up with an initial speed of 22.5m/s. How high does the ball rise? If the ball is caught at the same distance above the ground how long was the ball in the air? • The current world record for vertical leap is 1.5m. What was this individual’s initial speed? During this jump how long was the person in the air?

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