WEBVTT
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Express 39 metres per second in kilometres per hour.
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In order to answer this question, we need to recall some of our standard conversions for distance and time.
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There are 1000 metres in one kilometre.
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This means that in order to convert from metres to kilometres, we need to divide by 1000.
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There are 60 seconds in one minute.
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There are also 60 minutes in one hour.
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This means that in order to convert from seconds to hours, we would need to divide by 60 and then divide by 60 again.
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This is the same as dividing by 3600.
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In this question, we’re told that the speed is 39 metres per second.
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And we want to convert this into kilometres per hour.
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We know that speed is equal to distance divided by time.
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The speed 39 metres per second can be written as 39 metres over, or divided by, one second.
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As already mentioned, to convert from metres to kilometres, we divide by 1000.
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39 divided by 1000 is 0.039.
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Therefore, 39 metres is the same as 0.039 kilometres.
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To convert from seconds to hours, we divide by 3600.
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Whilst we could write one divided by 3600 as a decimal, in this case, it is easier to leave it as a fraction.
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Our final step is to divide 0.039 by one over 3600.
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Dividing by a fraction is the same as multiplying by the reciprocal of the fraction.
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Therefore, we can multiply 0.039 by 3600.
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This gives us an answer of 140.4.
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We can therefore say that 39 metres per second is the same as 140.4 kilometres per hour.
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An alternative method here would be to use the conversion from metres per second to kilometres per hour directly.
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One metre per second is equal to 3.6 kilometres per hour.
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This means that we can convert from metres per second to kilometres per hour by multiplying by 3.6.
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We arrive at 3.6 as 3600 divided by 1000 is 3.6.
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In this question, we could’ve multiplied 39 directly by 3.6 to give us our answer of 140.4 kilometres per hour.