Bullet fired and penetrates a block of wood

  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

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    Last edited: May 14, 2009
  2. jcsd
  3. am i even in the right direction? If not where did I go wrong?
     
  4. Doc Al

    Staff: Mentor

    Did you give the correct attachment?
     
  5. haha oops good catch give me a second
     
  6. now its the correct image. Thank you for that.
     
  7. Doc Al

    Staff: Mentor

    Hint: Use energy considerations.
     
  8. Is that the only way that we are able to solve this because we haven't gone over engeries in class yet?
     
  9. Doc Al

    Staff: Mentor

    No, you can also use dynamics/kinematics. Start by finding the average acceleration.
     
  10. 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. 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. LowlyPion

    LowlyPion 5,337
    Homework Helper

  13. 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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