Graphs of Motion · 7.1.3
Solving distance-time graph problems
Students apply distance-time graphs to solve multi-step problems, such as finding the average speed over the whole journey, determining when and where two moving objects meet, or calculating an unknown distance, time or speed using information read from the graph.
The official learning standard (7.1.3)
“Solve problems involving distance-time graphs.”
What it means
Students apply distance-time graphs to solve multi-step problems, such as finding the average speed over the whole journey, determining when and where two moving objects meet, or calculating an unknown distance, time or speed using information read from the graph.
How it is examined
A Paper 2 structured question, often the final part of a distance-time graph question, asking students to compute average speed, compare two journeys plotted together, or find the time and position at which two graphs intersect, representing when two objects meet.
Worked example
Using the graph from the previous example (car travels 60 km in 2 h, rests for 1 h, then returns 60 km in 1.5 h), find the average speed for the whole journey.
- Total distance travelled = 60 + 60 = 120 km (going out and returning).
- Total time taken = 2 + 1 + 1.5 = 4.5 hours.
- Average speed = total distance ÷ total time = 120 ÷ 4.5.
- Average speed = 26⅔ km/h ≈ 26.7 km/h.
Source:DSKP KSSM Mathematics Form 4 and 5 (Versi English)
Frequently asked questions
How is average speed different from the speed shown by one segment?
Average speed considers the entire journey's total distance and total time together, while a segment's speed is only the gradient of that one part of the graph.
How do I find when two objects meet on a distance-time graph?
Look for the point where the two graphs intersect; the time coordinate gives when they meet and the distance coordinate gives where they meet.
Do I include rest periods when calculating average speed?
Yes, rest periods count as part of the total time taken, even though no distance is covered, since average speed uses the whole journey's duration.