Step by step
The question
Question: the distance-time graph joins (0, 0) (4, 100) (6, 100) (10, 150), find the average speed.
distance-time graph: (0, 0) (4, 100) (6, 100) (10, 150)
1 Read the graph
Across: the time in seconds.
Up: how far from the start, in m.
Going up: moving away from the start.
Flat: stopped.
Going down: coming back.
2 Total distance and time
Add up how far it went in each part, going and coming back: 150 m.
Flat parts add nothing.
total distance = 100 + 50 = 150 m
The whole trip took 10 s, stops too.
total time = 10 s
Careful!
The time when it stopped is part of the trip.
It goes in the total time.
Careful: the stops count in the time
3 Average speed
Average speed is the total distance divided by the total time: 15 m/s.
average speed = 15010 = 15 m/s
4 Check
Let's check: 15 times 10 gives back the total distance, 150.
So it is right!
15 × 10 = 150
Let's look back.
First: read the graph.
Then: total distance and time.
Then: average speed.
Last: check.
Answer
average speed = 15010 = 15 m/s