Key ideas

• Distance: how far an object moves. Usual units: metres (m), kilometres (km).
• Time: how long the movement takes. Usual units: seconds (s), minutes (min), hours (h).
• Speed: how fast something moves. Formula: speed = distance ÷ time.
• Common speed units: metres per second (m/s) and kilometres per hour (km/h).

Important formula

Use the triangle to remember:

Units and easy conversions

• 1 km = 1000 m
• 1 hour (h) = 60 minutes = 3600 seconds
• To convert km/h to m/s: divide by 3.6 (because 1000 ÷ 3600 = 1 ÷ 3.6)
• To convert m/s to km/h: multiply by 3.6

Quick examples:

• 72 km/h = 72 ÷ 3.6 = 20 m/s
• 10 m/s = 10 × 3.6 = 36 km/h

Worked examples (step-by-step)

Kenyan context examples

• Nairobi to Thika is about 50 km. If a matatu takes 1 hour, average speed ≈ 50 km/h.
• On a tarmac road speed limit might be 80 km/h. If you travel 40 km at 80 km/h, time = 40 ÷ 80 = 0.5 h = 30 minutes.

Practice questions

1. A cyclist covers 24 km in 2 hours. Find the speed in km/h and in m/s.
2. A bus travels at 90 km/h. How long does it take to travel 270 km?
3. A runner's speed is 5 m/s. How many km/h is this?
4. If a car goes 60 km in 0.75 hours, what is its speed in km/h?

Answers (check your work)

1. Speed = 24 ÷ 2 = 12 km/h. In m/s: 12 ÷ 3.6 = 3.33 m/s (≈ 3.3 m/s).
2. Time = Distance ÷ Speed = 270 ÷ 90 = 3 hours.
3. 5 m/s to km/h: 5 × 3.6 = 18 km/h.
4. Speed = 60 ÷ 0.75 = 80 km/h.

Tips & common mistakes

• Always keep units correct before calculating. Convert km to m or hours to seconds when necessary.
• Remember divide by 3.6 to convert km/h → m/s and multiply by 3.6 for the reverse.
• Average speed does not tell you about stops. If there are stops, use total distance ÷ total time (including stops).