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Problem with bucket pulley

  1. Oct 12, 2009 #1

    VVV

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    A window washer pulls herself upward using the bucket-pulley apparatus shown in Fig. 4-48.(heres the pic. http://img126.imageshack.us/i/physcis.jpg/) The mass of the person plus the bucket is 70 kg.
    (a) How hard must she pull downward to raise herself slowly at constant speed?
    (b) If she increases this force by 8%, what will her acceleration be?
    For some reason i got wrong answers 686.7 N and 10.59 m/s^2, Why?
     
  2. jcsd
  3. Oct 13, 2009 #2

    Doc Al

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    Staff: Mentor

    Don't just give your answers--show how you got them.

    Hint: What's the relationship between how hard she pulls on the rope and the tension in the rope? How many times does the rope pull up on the "person+bucket" system?
     
  4. Oct 13, 2009 #3
    Hi! I am actually working on a question that is pretty much identical, with different number for weight and % of increase. I was able to get part A.. F=m*a, but then you divide the answer by 2, because the force is split on either side of the pulley. I'm having trouble with B though. I tried to sub in the new force (answer+10.1%... or whatever % was in your question) and solve for acceleration using the same formula F=ma, but I'm still not getting the right answer. Please help!!!
     
  5. Oct 13, 2009 #4

    Doc Al

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    Staff: Mentor

    Don't forget that F stands for the net force and that gravity doesn't change.
     
  6. Oct 13, 2009 #5
    I'm confused??? If the acceleration remains the same (9.8) then how do I solve for a??? And what other forces would be included in the net force???
     
  7. Oct 13, 2009 #6

    Doc Al

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    Staff: Mentor

    The force of gravity--the weight--remains the same, not the acceleration!
    Just the weight and the force from the ropes.
     
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