Recall and use the equation average speed = total distance travelled / total time taken

What is Average Speed?

Average speed is the total distance you travel divided by the total time you take. It tells you how fast you moved on average over a whole journey, not just at a single instant.

Formula

Use the simple equation:

$$v_{\text{avg}} = \frac{d}{t}$$

where $d$ is the total distance (in metres, kilometres, etc.) and $t$ is the total time (in seconds, hours, etc.). Make sure the units match.

Analogy & Example 🚗🏃‍♂️

Imagine you’re on a road trip from City A to City B. If you drive 150 km in 3 h, your average speed is the same as the speed you would need to maintain to finish the trip in that time, even if you speed up or slow down along the way.

Calculation:

1. Distance: 150 km
2. Time: 3 h
3. Average speed: $v_{\text{avg}} = \dfrac{150}{3} = 50$ km h^-1

Practice Problem 🧠

A cyclist travels 90 km in 4.5 h. What is the average speed?

Solution:

$$v_{\text{avg}} = \frac{90}{4.5} = 20 \text{ km h}^{-1}$$

Step‑by‑Step Checklist

1. Read the question carefully and identify the total distance and total time.
2. Check that the units for distance and time are compatible (e.g., both in metres and seconds, or kilometres and hours).
3. Insert the values into the formula $v_{\text{avg}} = \dfrac{d}{t}$.
4. Perform the division and write the answer with the correct units.
5. Double‑check the calculation and units before finalising your answer.

Exam Tips 📚

• Always show your working – examiners want to see the steps.
• Use the correct significant figures as given in the question.
• When units are mixed (e.g., km and s), convert first or use a conversion factor.
• Remember: average speed is a scalar, so direction does not matter.
• Check that your answer makes sense – e.g., a speed of 200 km h^-1 for a school bus is unrealistic.