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Velocity. Chapter 2, Section 1b. Average Velocity. Average velocity is displacement divided by the time interval. The units can be determined from the equation. SI Units: m/s Other Possible Units: mi/h, km/h, cm/year. Classroom Practice Problems .
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Velocity • Chapter 2, Section 1b
Average Velocity • Average velocity is displacement divided by the time interval. • The units can be determined from the equation. • SI Units: m/s • Other Possible Units: mi/h, km/h, cm/year
Classroom Practice Problems • A car travels 36 km to the north in 30.0 min. Find the average velocity in km/min and in km/h. • Answer: 1.2 km/min to the north or 72 km/h to the north • A car travels 100.0 km to the east. If the first half of the distance is driven at 50.0 km/h and the second half at a 100.0 km/h, what is the average velocity? • Answer: 66.7 km/h to the east
Speed • Speed does not include direction while velocity does. • Speed uses distance rather than displacement. • In a round trip, the average velocity is zero but the average speed is not zero.
Practice Problem • James walks 4 meters East, 2 meters South, 4 meters West, and 2 meters North. The entire motion lasted for 24 seconds. Determine the average speed and the average velocity. • Average speed was 0.5 m/s • Average velocity was 0 m/s
Practice Problem • What is the skiers average speed? Average velocity? • Average speed = 140 m/min • Average velocity = 47 m/min, right
Graphing Motion • How would you describe the motion shown by this graph? • Answer: Constant speed (straight line) • What is the slope of this line? • Answer: 1 m/s • What is the average velocity? • Answer: 1 m/s
Graphing Motion • Describe the motion of each object. • Answers • Object 1: constant velocity to the right or upward • Object 2: constant velocity of zero (at rest) • Object 3: constant velocity to the left or downward
Instantaneous Velocity • Velocity at a single instant of time • Speedometers in cars measure instantaneous speed. • Determined by finding the slope at a single point (the slope of the tangent) • What is the slope of the tangent line at t = 3.0 s? • Answer: approximately 12 m/s • What is the instantaneous velocity at t = 3.0 s? • Answer: approximately 12 m/s
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