Graphs of Motion
Average speed
Total distance divided by total time over a journey.
| English | Average speed |
|---|---|
| Bahasa Melayu | Laju purata |
| 中文 | 平均速率 |
How it is used
A cyclist rides 40 km in the first hour, rests, then rides 60 km, taking 3 hours in total. Average speed = total distance ÷ total time = (40 + 60) ÷ 3 = 100 ÷ 3 ≈ 33.3 km/h.
Where it shows up in SPM
In Graphs of Motion (Form 5) and word problems on speed. Both papers use it.
A common Paper 2 trap gives different speeds for different stages and expects total distance ÷ total time, not the average of the two speeds.
Don't confuse it with
Open the chapter: Graphs of Motion →
Frequently asked questions
Why can't I just average the two speeds?
Because the object spends different amounts of time at each speed. If it goes 60 km/h for 1 h and 20 km/h for 3 h, the total is 60 + 60 = 120 km in 4 h, so average speed = 30 km/h, not (60 + 20) ÷ 2 = 40 km/h.
Do resting times count in average speed?
Yes. Total time must include every part of the journey, resting periods included.
If a trip covers 120 km but includes a 1-hour stop within a 4-hour total, average speed is still 120 ÷ 4 = 30 km/h.