Average Speed

 Background: Average Speed is the distance traveled divided by an elapsed time. For instance, if you travel 100 miles in 2 hours, your average speed would be 50 miles/hour. Here is the formula we will use:

 Average Speed =  Distance                              Time = “change in” or “difference of”

Here is another way of looking at the formula:

 Average Speed = d2 – d1 t2 – t1  1)     A moon rock is dropped from a cliff and it takes 2 seconds for the rock to fall 6.6 meters. What is the moon rock’s average speed?

 Average Speed = Distance = 6.6 - 0 =   6.6 = 3.3 m/s Time 2-0 2  2) A boy rolls down a hill on a skateboard. At time = 4 seconds, the boy has rolled 6 meters from the top of the hill. At time = 7 seconds, the boy has rolled to a distance of 30 meters. What is his average speed? See the table below:

 Time (Seconds) Distance Rolled (Meters) 4 seconds 6 meters 7 seconds 30 meters

 Average Speed = Distance = d2 – d1 = 30 - 6 = 24 = 8 m/s Time          t2 – t1 7- 4 3  3) Analyze the following table of data of an accelerating car and calculate the speed for the two adjacent intervals.

 Time (seconds) Distance (cm) Speed (cm/s) 6 27.2 7 62.9 ?

 Average Speed = Distance = d2 – d1 = 62.9 – 27.2 = 35.7 = 35.7 cm/s Time          t2 – t1 7- 6 1

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