Speed · Usually met around P6
Converting speeds
Change distance and time separately.
How to do it
Method
Change distance and time separately
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, and 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). Going back: 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, and m/min to m/s is ÷ 60. A shortcut: km/h to m/s is ÷ 3.6, and m/s to km/h is × 3.6, because 3600 ÷ 1000 = 3.6: 72 ÷ 3.6 = 20.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
1620 m/min = ? m/s
Show the answer and working
Answer: 1620 m/min = 27 m/s
1620 m/min is 1620 m a minute; 1 minute = 60 seconds: 1620 ÷ 60 = 27, 27 m a second, so 27 m/s
Example 2
30 m/s = ? m/min
Show the answer and working
Answer: 30 m/s = 1800 m/min
30 m/s is 30 m a second; 1 minute = 60 seconds: 30 × 60 = 1800, 1800 m a minute, so 1800 m/min
Example 3
3 km/h = ? m/min
Show the answer and working
Answer: 3 km/h = 50 m/min
3 km/h is 3 km an hour; 1 km = 1000 m: 3 × 1000 = 3000, 3000 m an hour; 1 hour = 60 minutes: 3000 ÷ 60 = 50, 50 m a minute, so 50 m/min
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