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Friday 8/23 Notes

Friday 8/23 Notes. For those who went on the band trip. 1. Average Velocity. The average velocity is the rate at which displacement occurs Usually t i = 0 Velocity and displacement are in same direction (+ or -) Units: m/s, mph. Average Velocity.

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Friday 8/23 Notes

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  1. Friday 8/23 Notes For those who went on the band trip

  2. 1. Average Velocity The average velocity is the rate at which displacement occurs • Usually ti = 0 • Velocity and displacement are in same direction (+ or -) • Units: m/s, mph

  3. Average Velocity • Average velocity equals the slope of the line joining the initial and final positions (on x-t graph)

  4. Problem Example 2.2 (page 30)

  5. 2. Instantaneous Velocity • Instantaneous velocity = the velocity at a specific point in time • Ex: Speedometer • The limit of the average velocity as the time interval becomes infinitesimally • short (Δt  0)

  6. Instantaneous Velocity • Instantaneous velocity is the slope of the tangent to the curve at the time of interest

  7. Note:The instantaneous velocity of a point on a line is the slope of the line it is on.

  8. 3. Constant Velocity • Velocity does not change over time • Ex: car on cruise control

  9. Speed • Speed is a scalar quantity • same units as velocity • total distance / total time • No direction required

  10. Example • My drive to school: Average Velocity vs. Instantaneous Velocity What is my average velocity?

  11. I live about 25 miles from school,and the drive takes about 30 minutes. During the trip, I drive 2 miles @ 30 mph, stop at a light for 1 minute, accelerate to 60 mph and continue for 20 miles, stop at a light for 1 more minute, drive 45 mph for 3 miles, and then park. What is my average speed?

  12. Answer: solve for time in each,then vavg = (total x) / (total t) • 2 mi @ 30 mph = 4 min • Stoplight = 1 min • 20 mi @ 60 mph = 20 min • Stoplight = 1 min • 3 mi @ 45 mph = 4 min Total X = 2 + 0 + 20 + 0 + 3 Total time = 4 + 1 + 20 + 1 + 4 Vavg = 25 mi / 30 min = 25 mi / 0.5 hr = 50 mi/hr

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