F=m*a is indeed force, but the 'a' and 'm' you have to consider is the acceleration and mass of the object that's been hit. Whatever the truck has been doing in the seconds, hours, or years prior to the impact is irrelevant.
true...very true. What the truck was doing is irrelevant and that is why the formula for force is irrelevant as if you look up the formula for acceleration, time is a variable. If you say time is not a factor, then you can't use the formula.
No, it can't. Joules is energy. Pressure is excertion of force. They are completely different things.
Try looking up formulas to convert Joules to ____. You will see that 1 Joule = 8.89.... PSI.
And you are also wrong in your conclusion. Let's consider a strike to the head, bareknuckle (small area) or with large boxing gloves. The smaller the target, the more localized damage. But the impact on the brain will be identical to the hit that was done with the gloves. Impact energy is transferred to the brain via the skull. How that energy got delivered to the skull (wide or small area) is irrelevant.
The kinetic energy is the same and eventually, the same amount of energy is delivered to the brain, but the brain was not the impact area. The impact area may have been the whole side of the head or just the temple, all depending on the type of strike.
I am giving you straight simple physics. If you don't believe the physics, go look up the formulas yourself and study up on what they mean.