# Homework Help: Distance a bullet will travel while shot underwater

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1. Sep 5, 2016

### Wanna_be_Feynman

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

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

where:
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. Sep 5, 2016

### PeroK

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.