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Energy pretty simple but I think I'm missing something

  1. Jan 24, 2007 #1
    1. The problem statement, all variables and given/known data
    A projectile that has a volume of 326.10cm^3 is fired with an initial kinetic energy of 2.11x10^3kJ. What is the initial velocity (m/s) of the projectile? The density of the projectile is 18.95g/cm^3.

    2. Relevant equations
    D = m/v
    E = (1/2)(m)(v^2)

    3. The attempt at a solution
    1) Use D=m/v to get the mass of the projectile. (6179.595g)
    2) Convert kJ to J. (2,110,000J)
    3) Use the equation E = (1/2)(m)(v^2) and substitute appropriate data.

    2,110,000 = (1/2)(6179.595)(v^2)
    2,110,000 = (3089)(v^2)
    683.06 = v^2
    sq.root(683.06) = sq.root(v^2)

    The final answer that I get is 26.13m/s. According to this online quiz, it says that I am getting the answer wrong, but I still have a few more tries.

    I don't see what the problem is here, I even tried to convert some of the data into different units, but nothing works. It might be some kind of computer or quiz server problem, so if no one finds anything wrong with what I did, I'll probably have to tell the professor. Any kind of help would be appreciated.
  2. jcsd
  3. Jan 24, 2007 #2
    it looks like you did it correctly, although I didnt check your button pushing. Maybe the online quiz is being grouchy about sig figs?
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