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Homework Help: 2 bullets fired at the same time - find kinetic energies

  1. Dec 9, 2008 #1
    1. The problem statement, all variables and given/known data
    Two bullets have masses of 4.7 g and 11 g, respectively. Each is fired with a speed of 39.0 m/s.
    a) What is the kinetic energy of the first bullet? Answer in units of J.
    b) What is the kinetic energy of the second bullet? Answer in units of J.
    c) What is the ratio K2/K1 of their kinetic energies?

    2. Relevant equations
    KE = 1/2 mv2

    3. The attempt at a solution
    KE = 1/2 * 4.7g * (39.02 m/s)
    and so on...

    However, I do not know why the site is telling me my answers are wrong!
  2. jcsd
  3. Dec 9, 2008 #2


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    Homework Helper

    Hi nn3568,

    Did you convert the mass units to kg before entering the answer (if you leave it in grams the answer will not be in joules)? If so, what did you get?
  4. Dec 9, 2008 #3
    Yes, I did convert it into kg when I did the problem again but the site still said I was wrong :(

    my answers thus far:
    3574.35 (w/o changing to kg)
    1.833 (no idea)
    35.7435 (change to kg)
    0.01 (from a bad source :( )
  5. Dec 9, 2008 #4
    OH i get what i did wrong. i messed up in converting!
  6. Dec 9, 2008 #5


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    Homework Helper

    Mind your significant digits.

    Too many may not be good.
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