take 8 bullets a second * .003kg = .024kg/s
.024kg/s * 740m/s = 17.76 (Kg*m)/s^2 aka 17.76 Newtons
17.76N / 4.45 = 3.99 lbs of force per second.
This answer doesn't seem plausible. I thought a person would be knocked off his feet by a bullet. Whats wrong with the above or please explain why it's correct!
nothing's wrong with the above and your conversion is correct.
doesn't seem like very much eh? the reason is b/c of what i explained in the other question.. if you plot a graph of the force versus time, it will look like this:
_____|___|___|___|___|___|___|___|_____
those sharp vertical lines represent the bullet impacts, and the rest of the time the force is zero. if you average over this time span, the number turns out to be very low. but the height of those peaks is very high because so much momentum is exchanged in a very short time! so force is kind of misleading. in physics the more meaningful way to talk about collisions is to talk about the momentum exchanged in a collision, which is called an "impulse" because it happens over such a short time.
put another way, the bullet has a momentum of m * v, or .003 kg * 740 m/s = 2.22 kg*m/s. think about what that means. it's like getting whacked in the chest with a 2.22 kilogram (around 4.5 lbs) object moving at 1 meter per second - pretty heavy and pretty fast!
and that's just one bullet. think about 8 of them hitting you every second. furthermore, 3 grams seems like pretty low estimate for the mass of a bullet. that's something like a .22 or a .25. consider that a .44 magnum bullet, which is the sort of gun that actually can knock you off your feet, has a mass of 250 "grains" which is closer to 16 grams. that's more like getting hit with a 10-kg object. that's like someone winding up and throwing a 22-lb weight at you!
so there you go. the averaging and the short time interval for the impulse is what's misleading you.