Step by step
The question
Question: the distance-time graph joins (0, 0) (1, 40) (2, 40) (3, 70) (5, 0), find the speed of each part.
1 Read the graph
Across: the time in hours.
Up: how far from the start, in km.
Going up: moving away from the start.
Flat: stopped.
Going down: coming back.
2 Speed of each part
Speed is the distance divided by the time.
On the graph that is the slope: up over across.
Part A: 40 km in 1 h.
40 divided by 1 is 40 km/h.
Part B is flat.
The distance does not change: 0 km in 1 h.
The speed is 0: stopped.
Careful!
The flat part is high on the graph, but height is distance, not speed.
Flat means stopped.
Part C: 30 km in 1 h.
30 divided by 1 is 30 km/h.
Part D: 70 km in 2 h, coming back.
70 divided by 2 is 35 km/h.
3 Check
Let's check: speed times time gives back each distance: 40 and 30 and 70.
So it is right!
Let's look back.
First: read the graph.
Then: speed of each part.
Last: check.