1. Regents Physics Mr. Rockensies
Velocity v Speed
Regents Physics
Mr. Rockensies

2. Speed Velocity Scalar quantity
A measure of the change in distance over time
Speed = distance/time
Measured in meters per second (m/s)
Example: 43 m/s
Velocity
Vector quantity
A measure of the change in displacement over time
Velocity = displacement/time
Measured in meters per second (m/s)
Example: 43 m/s North
**Can be resolved into horizontal and vertical components

3. Average Speed
Obtained by summing all of the distances travelled and dividing by the total time.
Ex: A runner jogs 3 m/s for 20 seconds and then sprints at 9 m/s for 80 seconds. What was the runner’s average speed?
(60m + 720m)/100s = 7.8 m/s

4. Average Speed
Vf + vi 2
This equation can be used to find average speed, but not average velocity. Because velocity takes direction into account, it is not easily averaged by the above method.

5. Practice
A car drives 450 km over the course of 2.5 hours. What is the car’s average speed in km/hr? m/s?
A girl kicks a soccer ball so that the ball leaves the ground with a velocity of 18m/s 32° above the horizon. What is the horizontal component of the velocity? What is the vertical component?
A car drives off a ramp elevated at an angle of 45°. It achieves a velocity of 37 m/s just before leaving the ramp. What is the car’s vertical velocity? What is its horizontal velocity?
A ball rolls with a speed of 2 m/s. When the ball rolls off the edge of the table, what is its horizontal velocity at the moment it leaves the table? What is its vertical velocity?

6. Average Velocity
Obtained by first finding the overall displacement of the object. Then, divide the displacement by the total time. Direction of velocity is the same as the direction of the displacement.
Ex: A deer fleeing a hunter runs 300 m North in 15 seconds, but doubles back and trots 50 m South for 60 seconds. What is the average velocity of the deer?
The displacement is 250 m North. The time is 75 s.
v=d/t
v=250m/70s
v=3.57 m/s North

7. Practice
A delivery truck drives 40 km North in an hour to drop off a package. It then travels 100 km East in another hour to make its final delivery. What is the magnitude and direction of the average velocity?
Answer: 107km/2hr = 70km/hr (Magnitude)
tanθ=70/140; θ=26.57° East of North
A crazed squirrel is feverishly trying to locate the acorns it buried before the winter. It scurries 40 m north, 60 m south, 33 m east, 54 m north, 21 m west, 93 m south, 23 m west, 71 m south, 83 m north, 38 m east. After running out of steam, the squirrel collapses due to having sprinted for 123 seconds. What is the magnitude and direction of the average velocity?
Answer: 54.2m/123s = 0.44m/s
tanθ=27/47; θ=29.88° East of South