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Homework Help: Finding the Velocity of a Bullet Inside the Barrel

  1. Nov 1, 2007 #1
    Ok, I'm not the best physics student and I may have bitten off a bit more than I can chew with this project

    I am trying to find the velocity of a bullet while it is inside the barrel of a gun at three different points.

    The mass of the bullet is 13g, and the Force acting on the bullet is about 206842710 N/m^2 (I think?)

    The barrel is 0.114m long, and I'm looking at three intervals (0.038m, 0.076m, 0.0114m)

    What I'm trying to find is the velocity as well as the kinetic and potential energy acting on the bullet.

    I am more or less stumped, can anybody help? This project is due tomorrow, I can't see myself sleeping much tonight.
  2. jcsd
  3. Nov 1, 2007 #2


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    You have the mass and the force (that's a very big number by the way), use Newton's law (F = m a) to find the acceleration. Are you assuming it is constant inside the barrel? What formula's do you know that relate velocity, position and time? If you have the velocity, you can plug it into the kinetic energy formula (what is it?)
    Good luck!
  4. Nov 1, 2007 #3
    I must have fudged my normal force. The acceleration is too fast by about two decimal places.

    p.s: Oh...er....sorry about putting this in the wrong forum.
    Last edited: Nov 1, 2007
  5. Nov 1, 2007 #4


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    206842710 N/m^2 or 206.8 MPa is a pretty good pressure.

    One needs the cross-sectional area of the bullet in order to find the force.

    F = P * A where A is the surface area normal to the pressure.
  6. Nov 1, 2007 #5
    Thanks a billion, but I figure out the problem through more...logical channels.

    I just did some more researched and used the velocity as a starting point, rather than using the Normal Force (in psi, no less)

    These numbers make much more sense to me:

    Velocity: 348 m/s
    Mass = 0.01kg
    Normal Force= 37868.132N
    Kinetic Energy= 608J
    Distance= 0.038M
    Acceleration= 3186813.2M/S^2
    Time= 0.0001092S

    Thanks for the help, everybody. I may need to call upon it again.
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