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Constant speed question

  1. Oct 27, 2012 #1
    1. The problem statement, all variables and given/known data


    In a typical bosun's chair problem (in which an individual is on a platform suspended in the air by a massless, frictionless rope- about a pulley- holding the opposite end of the rope) one asks what pulling force is required to set the bosun chair (and person) into movement at a constant speed. I understand the mechanics behind the problem. My question is: how do you determine this constant speed? What- if anything- can you do to change the speed from, say, 0 m/s (which it intuitvely seems it would be) to 10 m/s without increasing the pull force (since this would cause the chair and individual to accelerate)?


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 27, 2012 #2

    Simon Bridge

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    If you change speed - you are accelerating.
    How is force related to acceleration?
     
  4. Oct 27, 2012 #3
    I think you're misunderstanding me. I am asking: how is it possible (if at all) to rise at DIFFERENT constant speeds? I.e. is it a possible scenario to rise in a bosun's chair at, say, 5 m/s or 22 m/s? If so, what is different (mechanically) in bringing about these differences in speed?

    EDIT* Ah, I understand your point now Simon- acceleration results since you would change velocity from zero to any positive quantity. After achieving your desired velocity (via accelerating), you could then return to applying the force which maintains that velocity.
     
  5. Oct 27, 2012 #4

    Simon Bridge

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    To maintain a velocity, you need a net force of zero. Otherwise you have it.
     
  6. Oct 27, 2012 #5

    tiny-tim

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    Hi Syrus! :smile:
    To change the speed, you increase or decrease the force for a short time, then go back to the "cruising" force. :wink:
     
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