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Questions on work done and Newton's third law

  1. Dec 19, 2012 #1
    Hello

    1- work done to push body forward is greater than to pull body backward
    what is the explanation for this?can you draw the two FBD in both cases ?



    2- why is nail driven in wooden wall but not in the concrete wall ؟ I guess this is somehow related to Newton's third law

    Thanks
     
  2. jcsd
  3. Dec 19, 2012 #2

    jedishrfu

    Staff: Mentor

    This seems like homework, you should provide some reasoning before we can help.
     
  4. Dec 19, 2012 #3
    No that's not a homework ..I thought of these questions by myself.

    as for the second question I'll tell you what I can imagine about this so far>>
    the hammer applies a force on the nail by pulling on it
    the nail has an equal reaction in the opposite direction
    the nail applies force on the wall
    the wall has an equal reaction in the opposite direction
    the force of the hammer on the nail is greater than the reaction of the wooden wall so the nail is driven in wood but that's not the case in concrete>>
    is my explanation true?if so why the reaction of the wall is different in wood and concrete?
    I hope it's a good evidence that my questions are not for homework
     
  5. Dec 19, 2012 #4

    jedishrfu

    Staff: Mentor

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