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Question On A Problem Don't Agree With Teacher

  1. Dec 12, 2006 #1
    1. Basic Physics stuff nothing too complex...

    #1. A clerk lifts a box 1m vertically. He also slides the box to an equal height over a 2m ramp. How much more force does it take to lift the box vertically?




    2. He stated that it would take something like twice as much(can't remember if this was it but doesn't really matter with my argument.) What I was arguing was the fact that we cannot tell how much force it takes to slide up the ramp due to the fact we have no coefficient of friction.

    For example...
    Would it take more force to lift a box or try to slide that same box over a ramp thats covered with tar or something with a very high coefficient of friction?




    3. I put not enough info as my answer and am wondering how on earth that cannot possibly be conceived as a correct answer...
    Thanks in advance...
     
  2. jcsd
  3. Dec 12, 2006 #2
    Well, to start, you could draw a diagram of the example. Since you are lifting the box in the question, is it necessary to have a coefficient of friction (whether static or kinetic)?
     
  4. Dec 12, 2006 #3
    Well I was thinking more in the lines of that the lifting doesn't matter so much as the sliding it up the ramp?
     
  5. Dec 12, 2006 #4
    The question relates to lifting, so wouldn't lifting actually matter? As I said, try to draw a picture of it. Remember, you're finding a force.
     
  6. Dec 12, 2006 #5

    cristo

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    I don't think you've stated the question correctly here- should it read something like "How much greater is the force required to lift the box vertically, than the force required to push the box up the ramp?"

    This is probably causing confusion in responses.
     
  7. Dec 12, 2006 #6
    Yeah, on the test it was asking for a ratio of sorts like twice as much etc
     
    Last edited: Dec 12, 2006
  8. Dec 12, 2006 #7
    Pardon me if I'm interpreting this wrong, but carbz I believe that the question is based solely on the relationships of the distance covered. So even if pclark were to draw a free-body diagram and plug in a hypothetical mass to solve the force required to lift the box, he'd be stumped at attempting to find the force to slide it up the ramp.
     
  9. Dec 12, 2006 #8
    All right. I figured that there must have been ratios involved. Anyway, the coefficient of friction isn't needed to determine the ratio of the two forces.
     
  10. Dec 12, 2006 #9
    Ok I just thought it might take more force if there was a high coefficiend of friction on the ramp... Thanks
     
  11. Dec 12, 2006 #10
    your welcome.

    Your teacher didn't give a coefficient of friction, so it must not play a role in the problem. If it was, then there would be more information to find it.
     
  12. Dec 12, 2006 #11

    Hurkyl

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    The problem was presumably meant to compare the amounts of force needed to overcome gravity -- not to consider other factors such as friction, wind resistance, lunar cycle, et cetera.


    P.S. this is a simple machines problem; if you know them, a free-body diagram would be unnecessary.

    P.P.S. or, it's a work-energy problem.
     
    Last edited: Dec 12, 2006
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