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Homework Help: Newton's laws?

  1. Jan 28, 2004 #1
    newton's laws????

    there is an athlete climbing a rope in gym class. he gets to a point halfway up the rope and is stationary. someone puts a bag of sand that is equal in weight to the athlete. they are both static and then the athlete starts to climb the rope, slowing and speeding up at random intervals.

    what happens to the bag of sand as he climbs?

    i was thinking that the bag of sand would move up a little bit as he was climbing slower and then down as he is climbing faster?

    am i right, or would the bag of sand stay at rest because they are the same weight?

    i'm thinking the first one...


  2. jcsd
  3. Jan 28, 2004 #2

    Doc Al

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    Re: newton's laws????

    Why do you think the bag will move up and down? (except for the shaking of the rope as he climbs) And what does the weight of the sand have to do with it?
  4. Jan 28, 2004 #3
    i think the problem is trying to imply that the bag is equal in weight to the athlete, implying that they are in static equilibrium initially. the problem states it explicitly and that is why i refered to it. thanks...

  5. Jan 28, 2004 #4
    i think as the climber reached the apex of the climb the bag would approach the floor.

  6. Jan 28, 2004 #5

    Doc Al

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    I'd be curious to see the exact statement of the problem. The bag doesn't have to be equal in weight to the athlete for there to be static equilibrium. Think about it: the athlete hangs from the rope; he's in static equilibrium because the forces on him (the rope pulling up on him & his weight pulling down on him) balance. No bag of sand needed.
  7. Jan 28, 2004 #6

    Doc Al

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    We must be thinking of totally different situations. How is the bag attached to the rope? How is the rope attached to the ceiling? Is there a pulley involved?

    I see no reason for the end of the rope to move---sandbag or not---as the man climbs up or down. (Ignoring the stretching of the rope.)
  8. Jan 28, 2004 #7
    i know. it seems that this problem has a case of ambiguity. i have given you the problem in its entirety leaving out some superfluous information, such as him, what, etc.

    i just wanted to see if anyone else could make sense of it.

    i would think that there would have to be a pulley involved, but it does not state it.

  9. Jan 29, 2004 #8


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    "someone puts a bag of sand that is equal in weight to the athlete"

    WHERE was the bag of sand put?? Was that part of the "superflous information" you left out?

    Was it attached to the climber?

    Was it tied on at the end of the rope?

    Was it tied to the other end of the rope after running it to a pulley? (Since the top of the rope was clearly attached to something when he began to climb, I would find that hard to accept.)

    Was it set on the floor next to the rope?
  10. Jan 29, 2004 #9

    today she said in class that she left out the part about the frictionless pulley.

    this makes the problem a little more reasonable.
  11. Jan 29, 2004 #10

    Doc Al

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    Ah... just as Halls and I suspected. So, why not take another crack at describing the exact problem and what you think the answer is. And---most importantly---why you think what you think. :smile:
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