Two cars are crash tested. Car A has a crumple zone, B doesn't. Both cars have mass 1500kg and a driver of mass 80kg and crash at 20m/s. Cars A and B take 0.8 and 0.2 seconds to stop respectively. Using this information, are crumple zones a necessity? (6)

We need to show that car A is safer than car B and this is done by showing that the force is greater on car B than car A.

Start by finding the force on car A, total mass 1580kg:

Force is the change of momentum / the time for which it acts.

Momentum before the crash = mv = 1580 x 20 = 31600kgm/s.

Momentum after = 0 as v = 0.

force = 31600/0.8 = 39500N (2)

Repeat this for car B and compare the results:

momentum before and after is the same

force = 31600/0.2 = 158000kgm/s (1)

Finally, to answer the question, finish with a closing statement such as: 'Car A has crumple zones which increase the collision time, this significantly reduces the force on the driver and makes the car much safer. Therefore crumple zones should be made a legal requirement' (3)