Compound co-ordinates: speed
A
B
C
D
E
F
G
H
I
J
Distance (m)
9
18
15
16
12
5
10
8
6
4
Time (s)
3
6
3
2
4
1
2
1
2
0.5
A moth, locust and housefly were timed to see how quickly they could travel 20m ... but the
results have been muddled up!
1. Plot the data on a graph, with time on the x-axis (up to 8s) and distance on the y-axis
(up to 20m).
2. Explain how your graph provides the times for each different insect, given that they
travelled at a constant speed. Add three lines to your graph to help.
3. Given that the locust was the fastest insect and the moth was the slowest, label each of
your lines. Give your graph an appropriate title.
4. Using your graph, find the following information for each insect to 1 decimal place:
a. the total time taken to travel 20m
b. the time taken to travel 10m
c. the time taken to travel 5m.
What do you notice about your answers? Explain. How long would it take each insect
to travel 2.5m?
5. What feature of the graph shows the speed of each insect? Calculate the three
speeds, giving your answers in m/s.
6. Given that the insects continue at a constant speed, calculate the following for each
insect (giving answers to 1 decimal place where appropriate):
a. the distance travelled after 10 seconds
b. the distance travelled after 20 seconds
c. the distance travelled after 21 seconds
d. the time taken to travel 25m
e. the time taken to travel 50m
f.
the time taken to travel 52.5m.
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Compound co-ordinates: speed
Teaching notes
This resource is designed to help students make sense of compound units by linking to
straight line graphs and proportion. The activity works best on graph paper, to provide more
accurate answers.
You may wish to provide more able students with the data in the table below instead, which
would require them to plot decimal values:
A
B
C
D
E
F
G
H
I
J
Distance (m)
20
9
4
6
20
3.6
6.5
9.6
6.3
5.4
Time (s)
4
1.8
0.8
0.75
2.5
1.2
1.3
1.2
2.1
1.8
Answers (key vocabulary in bold)
1. (Note that variables must be placed this way round on the axes so the speed can later
be calculated from the gradient of the line. The decimal data should produce lines with
the same gradients.)
distance
(m)
time (s)
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Compound co-ordinates: speed
2. The points lie on three straight lines going through the origin – since the insects
travelled at constant speeds, each line represents the speed of each insect. This
shows that the distance travelled is proportional to the time. Students should add the
lines to their graph as shown above.
3. The locust was fastest, so took the least time to travel 20m, therefore is represented by
the steepest line. The moth was the slowest, so took the most time, and therefore is
represented by the shallowest line. The housefly must be the remaining line.
4. (Note that these answers have been calculated from the speeds. Students will read
their answers from the graph, so they may not be as precise)
Locust
Housefly
Moth
a.
20m
2.5s
4s
6.7s
b.
10m
1.3s
2s
3.3s
c.
5m
0.6s
1s
1.7s
As the distances are halved, the times are halved (roughly, since values are rounded to
1d.p.). The insects are travelling at a constant speed, so their times are in
proportion. If the distance is halved again to 2.5m, the times will also be halved:
2.5m
Locust
Housefly
Moth
0.3s
0.5s
0.8s
5. The speed is shown by the gradient of the lines. Students could discuss whether to
calculate the speeds from the gradients, or direct from the data:
Locust
distance (m)
speed 
time (s)
Housefly
distance (m)
speed 
time (s)
Moth
distance (m)
speed 
time (s)
15
3
 5 m/s
16
2
 8 m/s
18
6
 3 m/s



6. Students could discuss whether they calculate from the speed each time, or whether
they calculate the first value then find the rest using proportion.
Locust
Housefly
Moth
a.
10s
80m
50m
30m
b.
20s
160m
100m
60m
c.
21s
168m
105m
63m
d.
25m
3.1s
5s
8.3s
e.
50m
6.3s
10s
16.7s
f.
52.5m
6.6s
10.5s
17.5s
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