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Homework Help: A bullet strikes a wooden block

  1. Oct 27, 2012 #1
    1. The problem statement, all variables and given/known data
    A 25 g bullet is fired at 150 m/s into a 2.0 kg block of wood hanging from a string 3.0 m long. The bullet becomes embedded in the block. To what height do the bullet and block swing?

    2. Relevant equations
    m1v1 = (m1+m2)vf
    1/2 mv^2 = mgh

    3. The attempt at a solution
    0.025 (150) = (0.025 + 2)vf
    vf = 1.85 m/s

    1/2 2.025 1.85^2 = 2.025 9.8 h
    h = 0.175 m

    I don't know what to do from here.
  2. jcsd
  3. Oct 27, 2012 #2
    First things first, try not to plug in numbers until after you get the final result. This reduces rounding error and can give you let you see how to do some of the algebra without having to deal with specific numbers.
    That being said, you seem to have done everything right. What do you mean "I don't know that to do from here." You were told to find the height and you found the height.
  4. Oct 27, 2012 #3
    So the length of the string doesn't matter?
  5. Oct 27, 2012 #4
    Yes. It would only matter if the height is more than twice the string length. If it then wants you to calculate the maximum angle or the oscillation frequency, then the string length would also matter.
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