Until the second half of the 20th century, cars were designed as strong rigid boxes, which designers thought would protect passengers in accidents. In fact, although average speeds were much slower than today, passengers were often very badly injured.
Modern cars are designed with safety features including 'crumple zones'. The crumple zones are at the front and rear of the car but do not include the passenger section. In a crash, the crumple zone is designed so that it deforms and bends. This is shown in Fig. 1.1.
The use of crumple zones explains why the front and rear of cars are badly damaged during accidents.
Another safety feature of modern cars is air bags. During a collision, air bags quickly inflate, filling the space between the driver and the steering wheel and windscreen. This is shown in Fig. 1.2.
Two cars are crash-tested to assess how much protection air bags provide in a road-traffic accident.
Car A does not have an air bag, whilst car B does.
Car A has a mass of 1200 kg and car B has a mass of 1500 kg.
Both cars have a driver of mass 70 kg and they both crash to a stop from an initial speed of 30 m/s.
At the moment of impact, the drivers are thrown forwards, taking different amounts of time to come to a stop. The driver of car A takes 0.3 seconds to stop, while the driver of car B takes 0.7 seconds to stop.
Â
Using this information, calculate the forces which would be experienced by the drivers due to the impact.
  Â
(i)
For the driver in car A
Force = .................................... N [3]
 Â
(ii)
For the driver in car B
Force = .................................... N [2]