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Homework Help: Newtons law theoroy question

  1. Sep 19, 2010 #1
    1. The problem statement, all variables and given/known data
    1.A 140 kg man pushes a 90 kg man. They are first motionless, as they push larger man moves smaller one backwards.
    which statement is correct.
    a)forces are always equal
    b) larger wrestles always exerts larger force
    c)when they are motionlesss forces are equal but as they start to move larger man exerts a larger force on smaller man exert man on him.

    3. The attempt at a solution
    According to newtons third law..every action force has an equal but pposite reaction force
    ..in that case the answer would be a)
    but than why is the smaller man moving back is it because the force of friction on the man has been overcome?
  2. jcsd
  3. Sep 20, 2010 #2


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    Yes, you are correct, but I think the problem should have been worded better: the force exerted by the larger man on the smaller man is always equal (and opposite) to the force exerted by the smaller man on the larger man.
    Yes, the net force on the smaller man is greater than zero, so the smaller man accelerates, per Newton 2; the net force on the larger man is zero, so the larger man does not move, per Newton 1.
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