Idea of Speed, Distance and Time
ICSE Class 6 · Mathematics · Chapter 17
What this chapter covers
- What speed means
- How speed, distance and time are linked
- Units of speed
- Changing km/h into m/s and back
- Daily-life problems on speed, distance and time
Key definitions
Distance is the length of the path that something covers as it moves from one place to another.
Time taken is how long the journey lasts, from the start to the finish.
Speed is the distance that something covers in one unit of time, such as one hour or one second.
A rate is a comparison that tells how much of one quantity goes with one unit of another quantity.
Kilometre per hour is a unit of speed that tells how many kilometres are covered in one hour.
Metre per second is a unit of speed that tells how many metres are covered in one second.
Key points
- Speed is the distance covered in one unit of time; it tells how fast something moves.
- For the same distance, less time means more speed; for the same time, more distance means more speed.
- Speed = Distance ÷ Time; Distance = Speed × Time; Time = Distance ÷ Speed.
- Units of speed join a distance unit and a time unit with "per": km/h and m/s are the most common.
- Before working out a problem, make the units match: km with hours, or m with seconds.
- To change km/h into m/s, multiply by 5/18; to change m/s into km/h, multiply by 18/5.
- Always write the unit with the answer.
Questions answered
A bus covers 150 km in 3 hours. What is its speed?
Speed = 150 ÷ 3 = 50 km/h.
Two runners finish a 200 m race. One takes 30 seconds and the other takes 34 seconds. Who is faster, and why?
The runner who takes 30 seconds is faster, because both covered the same distance and that runner took less time.
A car moves at 60 km/h for 3 hours. How far does it travel?
Distance = 60 × 3 = 180 km.
A cyclist rides 24 km at 8 km/h. How long does the ride take?
Time = 24 ÷ 8 = 3 hours.
Change 72 km/h into m/s.
72 × (5)/(18) = 4 × 5 = 20, so the speed is 20 m/s.
Change 15 m/s into km/h.
15 × (18)/(5) = 3 × 18 = 54, so the speed is 54 km/h.
A man walks at 6 km/h for 20 minutes. How far does he walk?
20 minutes = 1/3 hour, so Distance = 6 × 1/3 = 2 km.
Name the two units of speed in this chapter, and say when each one is used.
Kilometre per hour (km/h), used for long journeys by road, rail or air; metre per second (m/s), used for short, quick movements such as a race.