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Originally Posted by XCPWSF
I was wondering about this just before and I can't remember any of my yar 11 physics stuff, but would hitting a solid imovable object at 100km/h be worse than hitting another car head on also travelling at 100km/h?
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Kinetic energy increases by the square of the velocity. A car travelling at 100 kph relative to an object has 25% of the kinetic energy compared to travelling at relative 200kph
Cars are made to absorb/convert impact energy by deflecting or compressing over an extended displacement. e.g. by buckling side frame crash boxes. This gives rise to vehicle crush stiffness coefficients. But because the F=ma law still applies the total % absorption depletes by the square of the velocity once again. A crash box might only need 100kN to buckle 100mm, a car doing 100kph is going to have a lot more force than that.
A solid immovable object ideally won't absorb any energy, but your chances are theoretically better hitting it at 100kph than another car head on doing the same speed, by a factor of about two.