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Homework Help: Immedaite Help Is required

  1. Feb 11, 2010 #1
    Hello every one, I wish if you could help with this problem :

    b]1. The problem statement, all variables and given/known data[/b]

    Given the following informaiton for a paritculart watershed, determine the amount of the annual precipitaion recieved

    2. Relevant equations

    water shed area : 4530 m^2
    average flowrate : 39.6 m^3/second
    Average infiltration 9.2 * 10 ^ -7 m/s
    Evapo-transpirtaiton : 45 cm/year
    change is storage -23.9 cm/year

    3. The attempt at a solution

    I am sure that the formula to solve this is : change in storage = input - output + prec. - Evaportaion .

    However, I have some doubts :

    First, I assumed that the Evapo-transpirtaiton is the same as : Evaportaion so I am going to substitute it in the formula .

    Second, which is the major :
    The units - do we need to convert the units ?
    My idea is to convert all cm to m but then when prec.is found : how to know if m/year

    or m/s ?

    Hope hearing replying soon =)
  2. jcsd
  3. Feb 12, 2010 #2


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    Just transform all to a single unit. No matter what transformation you make if you have a single set of units the result will be right. And after you can transform the result in any unit system you want or anything that fits better, m/year maybe.


    m instead of any other lenght unit
    year instead of second .......as at such a surface area the second seems small.
  4. Feb 12, 2010 #3
    so, you're saying that I need to make all cm to m and all seconds to years.

    But the numbers will be sooo big because there are a really huge amount of seconds in one year ..

    So, is that ok ?
  5. Feb 12, 2010 #4


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    Staff: Mentor

    That's where the scientific notation (6.02x1023) comes in handy.
    Last edited by a moderator: Aug 13, 2013
  6. Feb 14, 2010 #5
    Ok, thnx I 'll try this >
  7. Feb 14, 2010 #6
    Borek you made me laugh :)
  8. Feb 14, 2010 #7
    But, what if I got powers with(-) sign ?
  9. Feb 15, 2010 #8


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    Staff: Mentor

    That's OK, that's part of the notation. Do you know what it means?
    Last edited by a moderator: Aug 13, 2013
  10. Feb 18, 2010 #9
    ya .. thnx alot
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