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Homework Help: Distance a bullet will travel while shot underwater

  1. Sep 5, 2016 #1
    1. The problem statement, all variables and given/known data

    I am trying to work out the problem:
    If I shoot an ak47 underwater with 7.62x39mm ammunition, how far will the bullet travel before coming to a stop?

    2. Relevant equations

    The equation that I have used to find the drag force is the drag equation:

    F =1/2 p*A*C_d*v^2

    p is the density of the water (1000 kg/m^3)
    v is the velocity of the bullet (730 m/s)
    A is the cross sectional area of the bullet with diameter 7.62mm
    C_d is the drag coefficient to which I am using 0.29 based from a website which had statistics about the bullet

    3. The attempt at a solution
    I have found this I get approximately 850, 000 N of force. I am then stuck as to how to calculate the distance the bullet travels before it stops.
  2. jcsd
  3. Sep 5, 2016 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Because the drag force varies with velocity, you will get a differential equation in ##v##. The drag force will not be constant. The first step is to derive this differential equation.
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