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Homework Help: Karate Punch

  1. Apr 14, 2009 #1
    1. The problem statement, all variables and given/known data
    I am working on a physics project about karate, and I want to know how fast I would have to punch to break a practice concrete slab.

    I know that the slab requires 1900 newtons to break. I also know that my arm has an approximate mass of 8.4 kg. I also know that my arm is about 80 cm long, which is basically the distance my punch will travel.

    2. Relevant equations

    F = ma

    3. The attempt at a solution

    If I simply use F = ma, it tells me that I must punch at 226 m/s to break the concrete...that doesn't seem right to be. I know I'm probably oversimplifying the problem...could someone point me in the right direction?
  2. jcsd
  3. Apr 14, 2009 #2


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    Science Advisor
    Homework Helper

    It's not just the mass of the hand/arm if there is muscle power behind it at impact
    I think you might have to consider the area of the impact, the concrete has a maximum stress (force/area=pressure) that might be more important than the ulitmate load
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