Distance-time graph: (0, 0) (2, 20) (3, 20) (4, 0), find the speed…

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) (2, 20) (3, 20) (4, 0), find the speed of each part.

distance-time graph: (0, 0) (2, 20) (3, 20) (4, 0)

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.

Speed is the distance divided by the time.

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

speed = distancetime = slope

Part A: 20 km in 2 h.

20 divided by 2 is 10 km/h.

A: speed = 202 = 10 km/h

Part B is flat.

The distance does not change: 0 km in 1 h.

The speed is 0: stopped.

B: speed = 01 = 0 km/h

Careful!

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

Flat means stopped.

Careful: not speed = 20 km/h ✗

Part C: 20 km in 1 h, coming back.

20 divided by 1 is 20 km/h.

C: speed = 201 = 20 km/h

Let's check: speed times time gives back each distance: 20 and 20.

So it is right!

10 × 2 = 20, 20 × 1 = 20

Let's look back.

First: read the graph.

Then: speed of each part.

Last: check.

Answer

C: speed = 201 = 20 km/h

Try this one yourself, then check:

distance-time graph: (0, 0) (2, 10) (3, 10) (4, 0)

Show the answer

A: 5 km/h, B: 0 km/h, C: 10 km/h