1. The problem statement, all variables and given/known data Force exerted on a car by a crash barrier as the barrier crushes is F=-(4.5+140s) kN where s is the distance in metres from the initial contact. If a car of mass 2000 kg is travelling at 100 km/h when it hits the barrier the barrier deformation required to bring the car to rest will be most nearly: 0.35,1.04,1.78,2.81,3.29 metres 2. Relevant equations Not entirely sure which to use here? Impulse => Fdt=mv1-mv0 or conservation of energy: 0.5mv^2+(F)ds = 0 3. The attempt at a solution 0.5mv^2+(F)ds = 0 0.5(2000)(27.78)^2+[-4.5s-70s^2] = 0, solve for s and i believe i got the incorrect answers (it is supposed to be 3.29m) any clues guys am i completely off in my method? thanks!