# friday 8/23 notes

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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 PresentationTRANSCRIPT

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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