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Change of units in a problem

  1. May 16, 2013 #1
    1. The problem statement, all variables and given/known data
    Calculate various fuel quantities for Flight 143. The plane already had 7682 L of fuel ob board prior to flight and tanks were to be filled so that a total of 22300 kg were present at takeoff

    (a) Using the incorrect conversion factor of 1.77 kg/L calculate in kg the amount of fuel that was added to the plane
    (b) Using the correct conversion factor of 1.77 lb/L calculate in kg the amount of fuel that was added to the plane
    (c) By what percentage would the plane have been underfueled

    2. Relevant equations
    No relevant equations as it is a simple conversion of units

    3. The attempt at a solution

    Solution for (a) was attempted by multiplying the existing fuel and subtracting it from the total amount of fuel .. answer was 8702 kg fuel needed
    (b) was attempted by converting the total amount into newtons by multiplying 9.81 and then converted to pound.. the answer found was 16134 kg

    Can someone please verify and let me know if the answers are correct
  2. jcsd
  3. May 17, 2013 #2


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    Gold Member

    I got roughly the same answers but I didn't do b) the same way.

    I converted 7682 L to 13579 Lbs then converted that to 6168kg (using 1kg = 2.2Lbs). Then subtracted 6168 from 22300 to give 16132 kg. I see no need to involve g.
  4. May 17, 2013 #3
    sorry for sounding a little ignorant but wt does lbs stand for?
  5. May 17, 2013 #4


    Staff: Mentor

    lbs = pounds

    This is an unusual abbreviation since there are no letters in the abbreviation (lb) that are also in the word that is abbreviated (pound). The origin of the abbreviation is the Latin word libra, a measure of weight about the same as one pound.
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