### Video Transcript

Express 39 metres per second in kilometres per hour.

In order to answer this question, we need to recall some of our standard conversions for distance and time. There are 1000 metres in one kilometre. This means that in order to convert from metres to kilometres, we need to divide by 1000. There are 60 seconds in one minute. There are also 60 minutes in one hour. This means that in order to convert from seconds to hours, we would need to divide by 60 and then divide by 60 again. This is the same as dividing by 3600.

In this question, we’re told that the speed is 39 metres per second. And we want to convert this into kilometres per hour. We know that speed is equal to distance divided by time. The speed 39 metres per second can be written as 39 metres over, or divided by, one second. As already mentioned, to convert from metres to kilometres, we divide by 1000. 39 divided by 1000 is 0.039. Therefore, 39 metres is the same as 0.039 kilometres. To convert from seconds to hours, we divide by 3600. Whilst we could write one divided by 3600 as a decimal, in this case, it is easier to leave it as a fraction.

Our final step is to divide 0.039 by one over 3600. Dividing by a fraction is the same as multiplying by the reciprocal of the fraction. Therefore, we can multiply 0.039 by 3600. This gives us an answer of 140.4. We can therefore say that 39 metres per second is the same as 140.4 kilometres per hour.

An alternative method here would be to use the conversion from metres per second to kilometres per hour directly. One metre per second is equal to 3.6 kilometres per hour. This means that we can convert from metres per second to kilometres per hour by multiplying by 3.6. We arrive at 3.6 as 3600 divided by 1000 is 3.6. In this question, we could’ve multiplied 39 directly by 3.6 to give us our answer of 140.4 kilometres per hour.