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Bullet fired and penetrates a block of wood

  1. May 14, 2009 #1
    1. The problem statement, all variables and given/known data[/b]

    A rifle with a barrel length of 61.54 cm fires a 8.17 g bullet with a horizontal speed of 400 m/s. The bullet strikes a block of wood and penetrates to a depth of 8.9 cm.
    What resistive force (assumed to be constant) does the wood exert on the bullet?


    2. Relevant equations
    Dynamics


    3. The attempt at a solution

    [​IMG]
     
    Last edited: May 14, 2009
  2. jcsd
  3. May 14, 2009 #2
    am i even in the right direction? If not where did I go wrong?
     
  4. May 14, 2009 #3

    Doc Al

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    Staff: Mentor

    Did you give the correct attachment?
     
  5. May 14, 2009 #4
    haha oops good catch give me a second
     
  6. May 14, 2009 #5
    now its the correct image. Thank you for that.
     
  7. May 14, 2009 #6

    Doc Al

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    Staff: Mentor

    Hint: Use energy considerations.
     
  8. May 14, 2009 #7
    Is that the only way that we are able to solve this because we haven't gone over engeries in class yet?
     
  9. May 14, 2009 #8

    Doc Al

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    Staff: Mentor

    No, you can also use dynamics/kinematics. Start by finding the average acceleration.
     
  10. May 14, 2009 #9
    Am i suppose to assume that the distance the bullet traveled is 70.44 cm? Which is the barrel length+ the depth of the bullet in the wood?
     
  11. May 14, 2009 #10
    I got the anwser it was 7343.822 N.....only problem is I dont know how I got it I found someone who did this problem online and just plugged my numbers in his equation but it doesn't show how he derived the equation!
     
  12. May 14, 2009 #11

    LowlyPion

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    Homework Helper

  13. May 14, 2009 #12
    I think working on physics so long actually made me worse at it. It was right in front of me I just needed you to remind me of Kinematics! just us xf=xi+(vf^2-vi^2)/2a....then multiply the mass of the bullet by acceleration and that gives me fs.....wow FML
     
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