5. A 1.20 ton school bus has 20 students and a driver on board with a mass of 50kg each and 80kg respectively. The bus is initially moving at 7.55 m/s and collides head on with electric post. Find the force exerted on the bus and its passengers assuming that (a) the bus is rigid and brought to a stop of 0.03s, (b) the bus has crumple zones and is brought to a stop in 0.45s. (6 points)