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Math Help - Question about man pulling thing without a pulley and with a pulley.

  1. #1
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    Question about man pulling thing without a pulley and with a pulley.

    In the first case A man is in a rased platform, he has a mass of 50kg, h's directly pulling a block of mass 25 kg, the floor below him can witstand a force of 700N, in the second case the smae man pulls the same block on the same platform have ing same withstand capacity of 700N, calculate the force exerted on the floor in both the cases and say which method is better.


    Now, obviously the second case is the best,

    But I can't seem to arrange each of the components in the formula

    Netforce = Resuiltant - Weight ( for first case that is )

    And for second case I compared it to a normal object falling down connected to a pulley in which the rope in the other side is connected to a less massive object, but I'm not sure...

    The correct answers are

    first case force on floor = 750N

    second case force on floor = 250N

    PLEASE HELP!, I don't want to know what the right anser is , I wANT to know the concept of this question properly....
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  2. #2
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    Hello ice_syncer
    Quote Originally Posted by ice_syncer View Post
    In the first case A man is in a rased platform, he has a mass of 50kg, h's directly pulling a block of mass 25 kg, the floor below him can witstand a force of 700N, in the second case the smae man pulls the same block on the same platform have ing same withstand capacity of 700N, calculate the force exerted on the floor in both the cases and say which method is better.


    Now, obviously the second case is the best,

    But I can't seem to arrange each of the components in the formula

    Netforce = Resuiltant - Weight ( for first case that is )

    And for second case I compared it to a normal object falling down connected to a pulley in which the rope in the other side is connected to a less massive object, but I'm not sure...

    The correct answers are

    first case force on floor = 750N

    second case force on floor = 250N

    PLEASE HELP!, I don't want to know what the right anser is , I wANT to know the concept of this question properly....
    In each case the tension in the rope = weight of block = 250N

    In the first case, when the man is pulling directly on the block, the end of the rope in the man's hand is exerting a downward force of 250N on the man. His own weight is exerting a downward force on him of 500N, so to keep him in equilibrium, the floor is required to exert a force of 500 + 250 = 750N. He's in trouble, if the floor can only withstand 700N!

    In the second case, where the rope passes over a pulley, the force exerted by the rope on the man is 250N upwards (assuming that the pulley is perfectly frictionless). So this time the floor must exert a force of 500 - 250 = 250N on the man, to keep him in equilibrium. Good - the floor can stand that!

    Do you see this OK now?

    Grandad
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