In a crash test a car of mass 1200 kg hits a wall and recoils. The initial velocity of the car is 20 m s and it bounces back at 1.5 m s as shown in Figure III. The contact with the wall lasts for 0.18 s. 20 m s' 1.5 m s O O O O Before After Figure III (i) What is the change of momentum of the car during this collision? (ii) Find the impulse of the force acting on the car. (iii) Sketch a graph to show the typical variation of force with time during a colli- sion like this and state what the area under the graph represents. (iv) Find the average force acting on the car during the collision. (v) Discuss why modern cars are designed to crumple in a head-on collision. Illus- trate your answer with a sketch graph (labelled CRASH 2) using the same scale as in part (b) (iii) to show how the force varies with time when a car crumples more than the one in the diagram. [12 marks]