Stage 10 · Percentages & speed
Converting speeds
Change the distance and time apart.
How to do it
Method
Change the distance and time apart
72 km/h: 72 × 1000 ÷ 3600 = 20 m/s
Another way
Shortcut: ÷ 3.6, × 3.6
72 ÷ 3.6 = 20; 20 × 3.6 = 72
In full
To change a speed's units, change the distance and the time separately: 1 km = 1000 m, 1 hour = 60 minutes = 3600 seconds. 72 km/h is 72 km an hour, which is 72 × 1000 = 72000 m an hour; that's 72000 ÷ 60 = 1200 m a minute, 1200 m/min, or 72000 ÷ 3600 = 20 m a second, 20 m/s. Back the other way: 20 m/s is 20 m a second, 20 × 3600 = 72000 m an hour, 72000 ÷ 1000 = 72, so 72 km/h. m/s to m/min is × 60, m/min to m/s ÷ 60. A shortcut: km/h to m/s is ÷ 3.6 and m/s to km/h × 3.6, since 3600 ÷ 1000 = 3.6: 72 ÷ 3.6 = 20 — the same answer.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
10 m/s = ? km/h
Show the answer and working
Answer: 10 m/s = 36 km/h
10 m/s is 10 m a second; 1 hour = 3600 seconds: 10 × 3600 = 36000, 36000 m an hour; 1 km = 1000 m: 36000 ÷ 1000 = 36, 36 km an hour, so 36 km/h
Example 2
144 km/h = ? m/s
Show the answer and working
Answer: 144 km/h = 40 m/s
144 km/h is 144 km an hour; 1 km = 1000 m: 144 × 1000 = 144000, 144000 m an hour; 1 hour = 3600 seconds: 144000 ÷ 3600 = 40, 40 m a second, so 40 m/s
Example 3
90 km/h = ? m/min
Show the answer and working
Answer: 90 km/h = 1500 m/min
90 km/h is 90 km an hour; 1 km = 1000 m: 90 × 1000 = 90000, 90000 m an hour; 1 hour = 60 minutes: 90000 ÷ 60 = 1500, 1500 m a minute, so 1500 m/min
Example 4
120 km/h = ? m/min
Show the answer and working
Answer: 120 km/h = 2000 m/min
120 km/h is 120 km an hour; 1 km = 1000 m: 120 × 1000 = 120000, 120000 m an hour; 1 hour = 60 minutes: 120000 ÷ 60 = 2000, 2000 m a minute, so 2000 m/min
Practise converting speeds in the game →Stage 10 · Percentages & speed · Free to start, unlimited questions, no download