[gurps] GURPS 4E MVA

[Anthony Jackson]

HK piter wrote:

> 5DR seems pretty high for a car, actually.

Standard bumpers can withstand a 2.5 mph impact with a wall without 
damage, so for a 53 hp vehicle that's (1.25 * 53 / 100) = 0.66 dice = 
1d-1 or 1d-2, and it's basically going to be never damaged, so DR 4-5 
isn't crazy, at least for the bumpers themselves; the rest of the front 
might be DR 1-2. This may mostly be a problem with the collision rules, 
though.

I'm not sure what sedan would have 53 hp, as that implies a weight of 
2300 lb or so. 60 hp (3,375 lb) is probably more realistic for a sedan. 
However, that doesn't actually matter that much.

For a 1,500 kg ground vehicle hitting a wall, energy at 2.5 mph (1.12 
m/s) is 940J, so we can probably assume the bumper is capable of 
handling a kilojoule impact.

Now, if instead we hit a 68 kg human while moving at 16.67 m/s, 
pre-collision KE is 208.4 kJ. After collision, velocity of combined 
system is 16.67 * (1500 / 1568) = 15.95 m/s, KE is 199.4 kJ, so the 
total energy in the collision is 9 kJ, which we can expect to cause 
significant damage to the car.

> From my own experience this does
> indeed sound right... provided the car was not one of the tin coffins
> that people drive these days but a real car, made properly.

Actually, a modern car with passenger compartment reinforcement and 
crumple zones provides superior protection to the occupants -- the 
crumple zone absorbs much of the impact, and then you have passenger 
compartment reinforcement that occurs after a lot of energy has already 
been dissipated. Oddly enough, it also does somewhat less damage to what 
you hit -- the basic point of the crumple zone is to take damage so that 
more important things don't have to.