# friday 8/23 notes

Post on 14-Jan-2016

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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. - PowerPoint PPT Presentation

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• Friday 8/23 NotesFor those who went on the band trip

• 1. Average VelocityThe average velocity is the rate at which displacement occurs

Usually ti = 0Velocity and displacement are in same direction (+ or -)Units: m/s, mph

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

• ProblemExample 2.2 (page 30)

• 2. Instantaneous VelocityInstantaneous velocity = the velocity at a specific point in timeEx: Speedometer

The limit of the average velocity as the time interval becomes infinitesimallyshort (t 0)

• Instantaneous VelocityInstantaneous velocity is the slope of the tangent to the curve at the time of interest

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

• 3. Constant VelocityVelocity does not change over timeEx: car on cruise control

• SpeedSpeed is a scalar quantitysame units as velocitytotal distance / total timeNo direction required

• ExampleMy drive to school: Average Velocity vs. Instantaneous Velocity

What is my average velocity?

• 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?

• Answer: solve for time in each,then vavg = (total x) / (total t)2 mi @ 30 mph = 4 minStoplight = 1 min20 mi @ 60 mph = 20 minStoplight = 1 min3 mi @ 45 mph = 4 minTotal 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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