Distance-time graph in m and min: (0, 0) (5, 400) (8, 400) (12, 0)…

Step by step, with the reason for every step · Distance-time graphs · Algebra 1

Step by step

Question: the distance-time graph joins (0, 0) (5, 400) (8, 400) (12, 0), find the speed of each part.

distance-time graph: (0, 0) (5, 400) (8, 400) (12, 0)

Across: the time in minutes.

Up: how far from the start, in m.

Going up: moving away from the start.

Flat: stopped.

Going down: coming back.

Speed is the distance divided by the time.

On the graph that is the slope: up over across.

speed = distancetime = slope

Part A: 400 m in 5 min.

400 divided by 5 is 80 m/min.

A: speed = 4005 = 80 m/min

Part B is flat.

The distance does not change: 0 m in 3 min.

The speed is 0: stopped.

B: speed = 03 = 0 m/min

Careful!

The flat part is high on the graph, but height is distance, not speed.

Flat means stopped.

Careful: not speed = 400 m/min ✗

Part C: 400 m in 4 min, coming back.

400 divided by 4 is 100 m/min.

C: speed = 4004 = 100 m/min

Let's check: speed times time gives back each distance: 400 and 400.

So it is right!

80 × 5 = 400, 100 × 4 = 400

Let's look back.

First: read the graph.

Then: speed of each part.

Last: check.

Answer

C: speed = 4004 = 100 m/min

Try this one yourself, then check:

distance-time graph: (0, 0) (5, 200) (8, 200) (12, 0)

Show the answer

A: 40 m/min, B: 0 m/min, C: 50 m/min