Unit 12 Lesson 6
Average Speed
Problems
What Is Motion?
Motion is when an object changes place or
position. To properly describe motion, you
need to use the following:
•
•
•
•
Start and end position?
Movement relative to what?
How far did it go?
In what direction did it go?
What Is Speed?
Speed is the distance an
object travels in a certain
amount of time.
To calculate speed, you
use the following formula:
Speed (s) = Distance (d)
Time (t)
Speed Math Problem
Suppose you ran 2 km in 10
min. What is your speed?
S = 2 km = 0.2 km/min
10 min
Another Problem
What is the speed of a car traveling
144 km in 90 minutes per hour?
________________ km/h
Solution
Km/hour:
How many hours are in 90 minutes? There are 60
minutes in 1 hour; therefore 90 minutes equals 1.5
hours
144 km = 96 km/h
1.5 hours
Ways To Calculate Speed
Constant speed is when
you are traveling at the
same rate of speed, such
as 55 mph constantly on
a highway.
Average speed is taking
the total distance
traveled, and dividing by
the total time it takes.
Used for calculations that
involve changing speed.
Instantaneous speed is
the speed at any one
given point in time.
Average Speed
Bass Boat Speed
140
Distance (meters)
What is the
AVERAGE
speed of the
bass boat
depicted in
the graph?
125
120
100
100
85
80
65
60
65
65
50
40
20
20
0
0
1
2
3
4
5
6
Time (seconds)
7
8
9
10
Average Speed
Bass Boat Speed
140
125
Distance (meters)
120
100
100
85
80
65
60
65
65
50
40
20
20
0
0
1
2
3
4
5
6
7
8
9
Time (seconds)
Average Speed = 125 meters = 15.6 m/s
8 seconds
10
Average
speed is
taking the
total distance
traveled (0 to
125 meters),
and dividing
by the total
time (1 to 9
seconds) it
takes.
Speed Graphs
Bass Boat Speed
70
65
65
65
Distance (meters)
60
50
50
45
40
30
20
20
15
10
0
0
1
0
2
3
4
5
6
7
8
9
10
Time (seconds)
•In what time period is the bass boat speeding up?
•In what time period is the bass boat slowing down?
•When is the speed NOT changing?
Graph the following data
Distance (meters)
30
60
90
120
150
Time seconds
15
30
45
?
?
Example of Average Speed
A track star runs the 5k (5
kilometers) race in 15 minutes (900
seconds). What is the average speed
of the runner?
V = total distance
/total time
V = 5000 m/900 s
Average Speed
(When
only
speeds
are
known)
If only speeds are known, then the average
speed is the sum of the speeds divided by
the total number of values.
FOR EXAMPLE: Find the average speed of
3m/s, 5 m/s and 8 m/s ?
Average speed = (3 + 5+ 8)/3 = 5.33 m/s
Word Problems
The distance between Pune and Nasik is 352 km. A bus
running at the speed of 40 km/hr left Pune at 8:00 AM.
What time will it reach Nasik?
TIME = DISTANCE  SPEED
44
4 hrs
44 hrs
352 km
=
8
=
=
5
5
40 km/hr
5
= 8 hrs and
1
12
4 X 60 min
5
= 8 hrs +
= 8 hrs and 48 min
4 hr
5
Homework Assignment
Pages 398 and 399
#1-26