Final answer:
A motorist's chances of survival are better with both a seat belt and shoulder harness due to impulse, which is used in car safety features like airbags and crumple zones extending the collision time and decreasing impact forces.
Step-by-step explanation:
A motorist's chances of surviving a collision are significantly improved if they are wearing both a seat belt and a shoulder harness. The underlying principle here is that of impulse, which concerns the change in momentum resulting from a force applied over a period of time.
In car safety, this principle is harnessed by employing features like dashboard padding and airbags that increase the time over which a stopping force is applied, thereby reducing the force's impact.
Cars also utilize crumple zones, wherein components made of plastic are designed to crumple upon impact, effectively prolonging the collision time.
This same concept is involved in the protection advantages offered by seat belts and shoulder harnesses, which secure the occupant firmly and spread out the forces over a larger area of the body to mitigate injuries. Moreover, the crumpling of racing cars, shifting away from rigid frames, has decreased fatalities in motorsport accidents by extending the collision duration and hence diminishing the forces.
Even outside of vehicles, the concept of impulse is significant. For example, bones are less likely to fracture when jumping onto a soft surface compared to a hard floor because the softer surface extends the collision time, thus lessening the impact force. Thus, an understanding of impulse and its applications in safety features can indeed be a lifesaver.