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Pulley question

  1. Feb 9, 2008 #1
    1. The problem statement, all variables and given/known data
    You wish to put your fridge on the second floor of your house (again).
    You decide to rig up a pulley system so as to not overexert yourself.
    Your maximum force is 250N and the fridge weighs 950N.

    a) diagram a pulley system using the fewest number of pulleys, which can achieve
    this feat
    b)The fridge must be raised 2.4 m, how far must you pull the rope?
    (Hint: you can still calculate this without the diagram)
    c) Calculate the work done using the pulley system and the work you
    would have done without the pulley system.
    d) What is the IMA of the system?
    2. Relevant equations
    W=F*D
    P= W/t
    AMA= FL/FA
    IMA= DA/DL
    EFFICIENCY= (work done by machine/work done on machine)x 100
    or
    EFFICIENCY= (AMA/IMA) * 100
     
  2. jcsd
  3. Feb 9, 2008 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Have you done anything at all? How about applying some of those equations?

    What "mechanical advantage" do you need? (In other words, how many times the maximum force you can apply is the weight of the fridge?) Since the total work you do does not change (conservation of energy) over what distance must you apply your maximum force to be equal to the "weight times distance" for the fridge?

    Your "relevant equations" are meaningless unless you know what the letters stand. I might guess that "W= FD" is "work", "force" and "distance" but what are "FL", "FA", "DA", and "DL"?
     
  4. Feb 9, 2008 #3
    wait

    I didn't do anything yet because our teacher did not teach us how to do problems with pulleys, or a problem like this in general.
    da: distance applied
    dl: distance load
    fl:force load
    fa:force applied.
    I just don't know how to start it, if I get a lead on how to do it I think I'll be able to get through it.
     
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