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Homework Help: Calculating force on a bullet, given mass + velocity + barrel length

  1. Jun 14, 2007 #1

    exi

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    1. The problem statement, all variables and given/known data

    An 8.9 g bullet leaves a rifle's muzzle at 456.6 m/s. The barrel is 0.5 m long.

    What is the force exerted on the bullet as it travels the length of the barrel? Answer in N.

    2. Relevant equations

    F = ma
    V = d/t (so T = d/v)
    a = v/t

    3. The attempt at a solution

    I tried to do this:

    1: T = d/v = 0.5 m / 456.6 m/s = 0.0011 s
    2: A = v/t = 456.6 m/s / 0.0011 s = 416967.12 m/s^2
    3: F = ma = 0.0089 kg * 416967.12 m/s^2 = 3711.0073 (kg∙m)/s^2

    No love.

    Anyone see anything glaringly wrong?
     
  2. jcsd
  3. Jun 14, 2007 #2

    Doc Al

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    Staff: Mentor

    The speed is not constant.
     
  4. Jun 14, 2007 #3

    Astronuc

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    Staff Emeritus
    Science Advisor

    So 456.6 m/s is the exit velocity, and the bullet started at zero velocity.

    Now what is it about force applied over distance, and what is the change in kinetic energy?
     
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