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Weird question about speed

I was doing some revision of the thermal stuff and I decided to have a go at the question in the purple box in the attached link but I don't see how part (a) can be worked out if we don't know any time values, can the time values be work out using the graph?


https://www.pearsonschoolsandfecolleges.co.uk/Secondary/Science/16Biology/ASandA2OCRBiology/Samples/A2StretchandChallengeSamplePages/Sp_1_3_2.pdf
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Avatar for Phichi
Phichi
11
Original post by Ki Yung Na
..


If you see lightning then start counting until you hear the thunder, it's quite easy to calculate. Lets say you count 10 seconds between the two. You know this corresponds to around 2 miles. To convert from miles to km, we multiply by roughly 1.6, and a further 1000 to meters.

Hence:

Distance=Speed×TimeDistance = Speed \times Time

Unparseable latex formula:

Speed = \dfrac{Distance}{Time} \, \, \, \Righarrow \, \, S_{sound} = \dfrac{2\times 1.6 \times 1000 }{10} = 320 ms^{-1}



Which is close to the actual value.
t5=s\frac{t}{5} = s
∴v=15Ms−1\therefore v = \frac{1}{5}Ms^{-1}
Convert from M to m to get the speed in ms-1​.
Original post by Phichi
...


Ah I see, so then whatever the number counted, the fraction will always be 1/5 x conversion?

Original post by morgan8002
t5=s\frac{t}{5} = s
∴v=15Ms−1\therefore v = \frac{1}{5}Ms^{-1}
Convert from M to m to get the speed in ms-1​.


Thanks, I actually did this but calculated some weird number but now I know I didn't convert it!

Thanks guys.
(edited 9 years ago)
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Avatar for Laura57
Laura57
8
awks, thought you wanted drug advice by the title...
Reply 5
Avatar for Phichi
Phichi
11
Original post by Ki Yung Na
Ah I see, so then whatever the number counted, the fraction will always be 1/5 x conversion?


Indeed. The distance in miles will always be t5\dfrac{t}{5}. If you wanted that in km, it'd just be 8t25\dfrac{8t}{25}
(edited 9 years ago)
Original post by Ki Yung Na
I was doing some revision of the thermal stuff and I decided to have a go at the question in the purple box in the attached link but I don't see how part (a) can be worked out if we don't know any time values, can the time values be work out using the graph?


https://www.pearsonschoolsandfecolleges.co.uk/Secondary/Science/16Biology/ASandA2OCRBiology/Samples/A2StretchandChallengeSamplePages/Sp_1_3_2.pdf


Read the question closely.

It says the distance in miles can be calculated by counting the seconds from the flash (instant the thunder is generated) until it can be heard and dividing that time in seconds by five to give an answer in miles.

Speed = distance / time = 1 mile / 5 seconds

1 mile = 1600 metres approx.

So approximate speed of sound in air using this method is 1600/5 = 320m/s

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