Distance-Time-Graphs Wjec-Eduqas Foundation

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Exam code:C300

Distance-time graphs

How do I use a distance-time graph?

Distance-time graphs show the distance travelled at different times
- Distance is on the vertical axis
- Time is on the horizontal axis
The gradient of the graph is the speed
- $speed space equals space distance over time space equals space rise over run$
The steeper the line the faster the object is moving
- Lines with positive gradients represent objects moving away from the start point
- Lines with negative gradients represent objects moving towards the start point
- Lines that are horizontal represent rest
  - The object is stationary (not moving)

How do I work out the overall average speed?

For journeys with multiple parts
- the overall average speed for the whole journey is $fraction numerator total space distance space travelled over denominator total space time end fraction$
- The total time includes any rests

Examiner Tips and Tricks

These questions often have a lot of parts that depend on each other, so always double check each answer before continuing.

Worked Example

One afternoon, Mary cycled 8 km from her home to her grandfather’s house.
Part of the travel graph for her journey is shown.

(a) Find Mary’s speed at 2 pm.

The speed is the gradient of the line at that point
The gradient at 2pm is the same as the gradient for all points between 1:45pm and 2:45pm
It is easiest to use $rise over run$ for that bigger section

$rise over run equals 6 over 1$

6 km/h

(b) Calculate, in minutes, how long Mary stopped on the way to her grandfather’s house.

The horizontal line is where Mary stops
The scale is 1 square = 15 minutes

15 minutes

(c) Calculate Mary’s overall average speed from leaving her home to arriving at her grandfather’s house, giving your answer correct to 3 significant figures.

Overall average speed is $fraction numerator total space distance space travelled over denominator total space time end fraction$

Total distance travelled is 8 km
Total time (including rests) is 1.75 hours

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Maths Gcse Wjec-Eduqas Foundation

Distance-Time-Graphs Wjec-Eduqas Foundation