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Fixed Pulley with Two Ropes

  1. Sep 16, 2008 #1
    1. The problem statement, all variables and given/known data
    There is a fixed pulley lifting weight of 2N. Attached to the weight there are two ropes. On the other side of the pulley there are two man standing, one of them just below the pulley and the other is further away (Illustrated). The weight is on balance, it is not moving. The man just below the pulley is using N force. What force the other man is using?


    2. Relevant equations



    3. The attempt at a solution
    I argue that the other man is also using force N. But my friend is saying that he is not.

    Any idea?

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  2. jcsd
  3. Sep 16, 2008 #2

    mgb_phys

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    Hard to really help without giving you the answer (especially since there are only two choices!)
    Hint - without friction, the tension in the rope is the same everywhere.
     
  4. Sep 16, 2008 #3
    That's what I am thinking (If I guessed your answer correctly). If there was only one rope, then one man would have to use 2N force. But since there are two ropes, each has to pull with N. But my friend is arguing that we need to find the composite force for two, because the angles are different. Isn't it on the pulley the force 2N. One is using N and the other should use N as well?
    This is not an assignment question by the way. Just for fun. We haven't seen any two rope pulleys before.
     
  5. Sep 17, 2008 #4

    stewartcs

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    The total combined load on the pulley would be 4N. For example, just imagine there was only one man pulling straight down on the rope on the other side with force 2N. Since the weight of the object is also 2N (straight down) and neither it nor the pulley are moving, the total reaction force on the pulley is 4N (draw a FBD and you see why if you don't already).

    CS
     
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