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Homework Help: Work And Power Problem

  1. Dec 20, 2004 #1
    I have a work and power problem but im not sure what it has to do with the work and power formulas and have no idea how to solve it.

    The question is

    with what speed can a lifting hoist rated at 12.6 kw raise a 326 kg load?

    i found distance to be 9401.94 but thats as far as i got

    help please

  2. jcsd
  3. Dec 20, 2004 #2


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    Science Advisor

    You found the "distance to be 9401.94"? What distance??

    12.6 kw is 12600 Joules per hour. In One Hour, it does 12600 Joules of work which corresponds to ( since w= mgh, (326)(9.81)h= 12600 ) 3.94 meters. It can only lift the 326 kg load at 3.94 meters per hour!
  4. Dec 21, 2004 #3
    Did you try using

    P = Fv
    W = Fx

    Because those two formula would give you the answer for velocity/speed by rearranging the variables around.
  5. Dec 21, 2004 #4


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    Homework Helper

    What hour...????????????????? :confused: U mean second... :wink: GDit.It gives the power:the power is force times speed.
    The power is 12.6 KW=12600W.The force is nothing but the gravity:
    F=mg=326kg*9.80665ms^(-2)=3196,9353N approx=3197N
    Speed is power over force:
    v approx=12600W/3197N approx=3.94 m/s.That is METERS PER SECOND... :wink:


    EDIT:The natural multiples of ten are usually noted by capital letters.
    [tex] 10^{3}\rightarrow K [/tex] apud "Kilo".Kg,Km,KW,KJ,KN,... :grumpy:
    Last edited: Dec 21, 2004
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