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Silly math problem (precipitation)

  1. Oct 11, 2007 #1
    Hello everyone. I have this simple math problem that is worth 5 marks and I am not sure if it is right. Anyway it is on precipitation, here it is!

    Record the amount of water (in centimetres) the tipping bucket rain gauge received. Calculate the total volume of water this would equal if this amount fell over the City of Guelph (area 86km squared). Is this volume greater or less than the average volume of water which flows through the city in the Spped River during a 24 hour period (average flow rate = 5.8mcubed per second).

    Okay so first I am having trouble calculating the volume, I dont know why:

    my recordings are: the amount of water (in centimetres) is four tenths of an inch--coverted equals 1.01600cm.

    so, can I calculate this by multiplying 1.01600 x 86km

  2. jcsd
  3. Oct 11, 2007 #2
    oops sorry i just read that i cant posthis here
  4. Oct 11, 2007 #3


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    If I understand this correctly- that there was no "funnel" to channel a lot of water into a small area (some rain guages are built that way to make it easier to read small amounts of water) then saying 1.016 cm fell on the bucket, then 1.016 cm would fall on every "bit" of the city. However, you cannot multiply 1.016 cm by 86 km- in fact there is no "86 km"; the area is 86 square kilometers. Convert 86 square kilometers to square cm Multiplying that by 1.016 cm will give the volume in cubic cm.
    Now you are told that the Spped River has a flow of 5.8 cubic meters per second. Convert 24 hours to seconds (there are 60 seconds per minute, 60 minutes per hour) and multiply by 5.8 cubic meters per second to determine the total flow in cubic meters. In order to compare that to the volume in cubic centimeters calculated above, either convert the cubic centimeter volume to cubic meters or vice-versa.
  5. Oct 11, 2007 #4
    THANKYOU!! I see now
  6. Oct 11, 2007 #5
    no nevermind, i dont think it is working out properly...hmm
  7. Oct 12, 2007 #6


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    Just make sure you use consuistant units whan finding the volume. If you have the area in meters_squared then multiply by the rain depth in meters to get volume in meters_cubed etc.

    Also when converting square or cubic units then make sure you use the appropriate power in the conversion. For example 1 m^2 is 100^2 cm^2 (10,000 square_cm) and 1 m^3 is 100^3 cm^3 (1000,000 cubic_cm). Failure to convert units correctly is a common source of error in this type of question.
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