The distance–time relationship — AQA GCSE Physics
Test yourself on The distance–time relationship with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
The distance–time relationship explained
Speed is distance divided by time, and that is exactly what a gradient is on this graph, so the two are the same calculation.
Read the full explanation
Pick two points far apart on the straight section, because a large triangle reduces the effect of reading error, and take the change in distance together with the change in time between them. A telescope's graph showing 38 km covered in 5.0 s gives a speed of 7.6 km/s. Mark schemes award one mark for reading a correct pair of changes, one for the substitution and one for the answer, so show all three steps. Read the axis units before dividing, because a vertical axis in kilometres and a horizontal axis in seconds give an answer in kilometres per second unless you convert first.
Your focus
- Calculate a speed from the gradient of a straight section of a distance-time graph.
- Select two widely separated points in order to reduce uncertainty in a gradient.
- Convert a gradient read in kilometres per second into metres per second.
The distance–time relationship exam tips
Marking Points
- one mark for reading a correct change in distance with the matching change in time
- one mark for a correct substitution into speed = change in distance divided by change in time
- one mark for the correctly calculated speed
- one mark for the unit that follows from the axes, converted where the question requires it
Examiner Tips
- 💡Draw the triangle on the graph itself; examiners give credit for the working shown there.
- 💡Choose points where the line crosses grid lines exactly so the readings are easy.
Common Mistakes
- dividing a single pair of coordinates rather than using the changes
- using a small triangle, so that reading errors dominate the answer
- taking a gradient across a curved section as though it were straight
- ignoring an axis marked in kilometres or in minutes