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Force of nail after being struck by a hammer

  1. Apr 13, 2009 #1
    1. The problem statement, all variables and given/known data
    A 5lb hammerhead, traveling at 5.4ft/s strikes a nail and is brought to a stop in .00081s. The acceleration of gravity is 32ft/s^2, What force did the nail recieve?

    2. Relevant equations
    The equation I have is F=Pf-Pi/delta T. Both Pf and Pi have a arrow above them going to the right.

    3. The attempt at a solution
    I know I have to find Pf and Pi, and P=mv. With that said would Pf be 0, since it comes to a stop, and Pi be (5lb)(5.4ft/s)? And I am guessing that delta T would .00081s?
  2. jcsd
  3. Apr 14, 2009 #2


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    Homework Helper

    Welcome to PF.

    The real question here is what is the mass of the hammerhead? Since they give you acceleration of 32ft/s2, then this suggests to me this is how much it weighs. So I would say you need to determine your mass as 5/32 and then multiply by your 5.4 to get your momentum and then proceed as you were apparently intending.
  4. Apr 14, 2009 #3
    So, p=mv which would be p=(5/32)(5.4) which equals .84375.
    Then, F=Pf-Pi/delta T, which would be (0)-(.84375)/(.00081)-(0), which would equal -1041.67 N, but you cant have a negative force can you? Am I doing this right, or am I missing something?
  5. Apr 14, 2009 #4


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    Which direction did you choose as + ?
    And what is the question asking?
    So if the impact of the hammer resulted in a (-) force to the hammer that sounds like it received an upward force and the nail received a downward force.
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