How Much Force Is Exerted on a Bullet When Fired from a Gun?

[bob24]

Homework Statement

A gun weighs 10lbs and the barrel length is 10.2 inches. It fires a .45 caliber bulect weighing .0328lbs at a speed of 918ft/s. How much force is exerted on the bullet when fired?

Homework Equations

F=ma

The Attempt at a Solution

Here is what I did. Keep in mind that it is wrong, but when I did it I believed it to the correct method.
Vi=0
vf=918
s=.85 ft
a=?
918^2=1.7a
a=495720ft/s(squared)

F=ma
F=.3105kg(495720)
F=153921.06 N

TRIED IT AGAIN:
MbAb=MgAg
(.001018634)(495720)=.3105a
a=1626.27
F=ma
F=(.3105)(1626.27)
F=504.95(aprox.)
Is this correct?

If not, what should I do instead?

 

[cordyceps]

F=ma
F=.3105kg(495720)

I think you switched to the metric system for the mass.

 

[bob24]

so was my 1st method right or was the second method right?

 

[cordyceps]

I'm not sure what your second method is. But the first method looks fine up to the F=ma.