QUOTE
Using your numbers plus what has been provided by others.
Muzzle Velocity : 900m/s
Bullet Weight : 0.063kg
x12 M249 Weight : 120kg
Troll Weight : 370kg
The force of the firing weapons is 900*0.063*12 = 680.4. Divide that by 490 and you have a movement of the troll of ~1.3m/s assuming all 12 weapons are firing simultaneously and we're ignoring other elements like recoil compensation, bracing, or various other effects.
Muzzle Velocity : 900m/s
Bullet Weight : 0.063kg
x12 M249 Weight : 120kg
Troll Weight : 370kg
The force of the firing weapons is 900*0.063*12 = 680.4. Divide that by 490 and you have a movement of the troll of ~1.3m/s assuming all 12 weapons are firing simultaneously and we're ignoring other elements like recoil compensation, bracing, or various other effects.
Well, first of all,
Amateurs
Troll changeling with 6 arms
Everyone fire as one in one giant dicepool co-op test wit 24 full auto covering fire lmg's.
Troll changeling with 6 arms
Everyone fire as one in one giant dicepool co-op test wit 24 full auto covering fire lmg's.
We're looking at 24 of these babies, not 12. And each of them is firing 20 rounds per pass, per the rules for suppresive fire. Secondly, muzzle velocity times bullet weight gets you bullet momentum, not force. To get force, you need to account for both bullet and gas momentum. The mass of expelled gasses is the same as your powder charge (or close enough) and is travelling at around half again the speed of the bullet. (Which is a very rough estimate. Call it between 125% and 175% of bullet speed.) Furthermore, bullet weights and charge weights aren't given in grams, but grains. Giving us about 4.1 gram bullets, and a 1.5 gram charge. So, total momentum absorbed by Dr. Dakka per pass is roughly 24*20*(900m/s)*(0.0041kg+1.5*0.0015kg) or 2743.2 m kg/s. Assuming a pass is one second, that's 2743 Newtons. Which, divided by mass, gives us 2743N/490kg = 5.6 m/s^2.
However, that ignores friction. It's a great result for the dude on rollerblades, but I was assuming the troll was nonsuicidal, and hence a reluctant participant. That knocks mu*weight off the force. For wet pavement+runflats, mu=0.3. Weight = 490kg*9.81m/s^2, so friction resistance = (490 kg)*(9.81m/s^2)*0.3 = 1440N. So net backward force = 2743N-1440N=1300N. Divide that by 490 kg, and you get 2.65m/s^2. Note that that's an acceleration rate. So he'll be going only 2.65 m/s after 1 s, 5.3m/s after 2s, etc.