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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

 

 

http://www.mansfieldct.org/schools/mms/staff/hand/lawsavevelocity2003_files/image008.gif

 


1)     A rock is dropped from a cliff and it takes 2 seconds for the rock to fall 6.6 meters. What is the rock’s average speed?

 

 

Average Speed =

http://www.mansfieldct.org/schools/mms/staff/hand/lawsavevelocity2003_files/image012.gif Distance

6.6 m – 0 m

=   6.6 m

3.3 m/s

 

* Time         

  2 sec – 0 sec

   2 sec

 

 

 

 

 

 

http://www.mansfieldct.org/schools/mms/staff/hand/lawsavevelocity2003_files/image015.gif

 

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 =

http://www.mansfieldct.org/schools/mms/staff/hand/lawsavevelocity2003_files/image019.gif Distance = d2 – d1

30 - 6

= 24

8 m/s

 

* Time          t2 – t1

7- 4

3

 

 

 

 

 

 

 

http://www.mansfieldct.org/schools/mms/staff/hand/lawsavevelocity2003_files/image015.gif


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 =

http://www.mansfieldct.org/schools/mms/staff/hand/lawsavevelocity2003_files/image026.gif Distance = d2 – d1

62.9 cm – 27.2 cm

= 35.7 cm

35.7 cm/s

 

* Time          t2 – t1

7 sec – 6 sec

1 sec

 

 

 

 

 

 

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