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Chapter 2

Chapter 2. Motion in one dimension (motion under constant acceleration). Motion under constant acceleration. Rewrite: Δ s = s - s 0. Reminder: Converting units. What is 10km/h in m/s ?. Example: Riding a bike. Bike: 10km/h originally Speed up for 10s At the end: 30km/h.

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Chapter 2

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  1. Chapter 2 Motion in one dimension (motion under constant acceleration)

  2. Motion under constant acceleration

  3. Rewrite: Δs = s - s0

  4. Reminder: Converting units What is 10km/h in m/s?

  5. Example: Riding a bike Bike: 10km/h originally Speed up for 10s At the end: 30km/h How far have I traveled?

  6. No a

  7. Landing a Jetliner Touch down: 270km/h Deceleration: 4.5m/s2 What is the length of the runway? Note a<0: deceleration

  8. No t

  9. Roller Coaster 1 Roller coaster: 9m/s in the beginning Distance in tunnel: 50m Acceleration: 8m/s2 How fast is it traveling when it comes out of tunnel?

  10. No t

  11. Roller Coaster 2 Roller coaster: 9m/s in the beginning Distance in tunnel: 50m Acceleration: 8m/s2 How much time does it take?

  12. No v

  13. Reminder: Quadratic Equation

  14. Roller Coaster 2: Easier way With this extra information, we can use any equation that contains t

  15. Acceleration due to Gravity g = 9.8m/s2, pointing down (always) (Note that g is defined to be a positive number)

  16. Same acceleration

  17. - + My Convention I usually pick the UP direction to be positive, the DOWN direction to be negative. With this convention, under free fall: a = -g = -9.8m/s2 Anything falling DOWN will have a negativevelocity.

  18. - + Warning People sometimes use the opposite convention. With this convention, under free fall: a = g = +9.8m/s2 Anything falling DOWN will have a positivevelocity. Be consistent with your convention and your answer will be correct.

  19. Dropping a ball Building height: 100m Time: 3s What is the initial velocity?

  20. No v Now that you know v0 you can then find v.

  21. Find v Building height: 100m Time: 3s What is thefinalvelocity?

  22. correct Conceptual Question A ball is thrown vertically upward. At the very top of its trajectory, which of the following statements is true: 1. velocity is zero and acceleration is zero2. velocity is not zero and acceleration is zero3. velocity is zero and acceleration is not zero4. velocity is not zero and acceleration is not zero

  23. Explanation The velocity vector changes from moment to moment, buts its acceleration vector does not change. Though the velocity at the top is zero, the acceleration is still constant because the velocity is changing.

  24. v0 Dennis Carmen v0 H vD vC Conceptual Question Dennis and Carmen are standing on the edge of a cliff. Dennis throws a basketball vertically upward, and at the same time Carmen throws a basketball vertically downward with the same initial speed.

  25. v0 Dennis Carmen v0 H vC vD Whose ball has a higher speed when it hits the ground? 1. Dennis' ball 2. Carmen's ball3. Same Same speed ≠ same velocity

  26. Dennis Carmen

  27. Correct:v2 = v02 -2gH v0 Dennis Carmen v0 H vA vB Whose ball has a higher speed when it hits the ground? 1. Dennis' ball2. Carmen's ball3. Same

  28. Frisbee v > 3m/s s = 6.5m-1.3m = 5.2m a = -9.8m/s2 Findv0

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