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# Average Speed

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Class Notes from Aug 24, 2011

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### Average Speed

1. 1. Good Morning!<br />Today we will:<br />review distance v time graphs as a model for motion<br />learn to calculate average speed<br />Please do NOW:<br />get a textbook, your lab book & your spiral<br />get out something to write with<br />
2. 2. Warm-Up<br />Draw the following graph in your lab book (include labels) and explain (in words) the motion it depicts<br />
3. 3. Modeling Speed: Equations<br />average speed can be found using the equation <br />sav=<br />where sav = average speed<br />Δd = change in distance<br />Δt = change in time<br />Δd<br />Δt<br />
4. 4. Modeling Speed: Equations<br />Sample Problem: If you drive a distance of 400 miles in 8 hours, what is your average speed?<br />
5. 5. Average speed<br />An average of 50 mi/h does not tell you your fastest speed or your slowest speed.<br />It does tell you that over a certain amount of time, you covered a specific distance<br />
6. 6. Average Speed<br />For instance, you probably weren’t traveling at a speed of 50 mi/h in your neighborhood, and you stopped at traffic lights, and on the freeway, you probably traveled faster than 50 mi/h.<br />
7. 7. Average Speed<br />average speed: total distance traveled in a specific amount of time<br />instantaneous speed: the speedometer reading at any given instant<br />constant speed: speed that does not change over a period of time<br />
8. 8. Equations<br />The formula for average speed ( sav = Δd/Δt) can also be used to solve for distance or time.<br />
9. 9. Sample Problem<br />You are traveling at 50 ft/s (about 35 mph) and your reaction time is 0.2 s. Calculate the distance you travel during your reaction time.<br />
10. 10. Equation Solving Strategy<br />In physics, when you do calculations it is very important to pay attention to the units you are using.<br />Always carry your units through the problem!<br />ALWAYS. REALLY. I’M NOT KIDDING.<br />
11. 11. Sample Problem #3<br />In an automobile collision, it was determined that a car traveled 150 feet before the brakes were applied.<br />If the car was traveling the speed limit of 40 mi/h (60 ft/s), what was the driver’s reaction time?<br />