How do you work out the force inflicted during a collision with a stationary pedestrian and a car travelling at 11.11m/s?

How can you calculate the force inflicted depending on the stiffness of the bumper on the car?

Also how can you calculate the new momentum of the car and pedestrian?

Thanks a lot, any help will be appreciated. Am desperate.

sounds like someones homework

no, well kind of. I'm a bit rusty on the calculations, and I'm off school, so I need help. I'm writing a 2000 word report.

To solve this problem, you need hugely more information, mostly about the physical properties and weight distribution of the pedestrian with respect to the bumper at the moment of impact. The stiffness of the bumper is likely to be relatively unimportant, compared to the stiffness of the pedestrian. If the bumper hits the pedestrian's legs, the effect will be quite different from hitting the pedestrian's center-of-gravity (as might be typical with a small child).

As a general rule, if the pedestrian absorbs relatively little energy in deforming, he/she will bounce off with nearly twice the vehicle's speed (i.e. 22 m/s) in the direction of travel of the vehicle. The integral of force over time will be equal to the change in momentum thus acquired. Typically, though, this collision is inelastic enough that the pedestrian absorbs quite a lot of energy in tearing flesh and breaking bones. In such a case, the pedestrian may acquire a speed close to that of the vehicle.

Regardless of the energy absorbed by the pedestrian, momentum is conserved. So the momentum of the car is reduced by the amount of momentum the pedestrian has after the collision. Because the car is normally much more massive than the pedestrian, its momentum reduction is quite modest, as a percentage of the total.

m1u1 + m2u2 = m1v1 + m2v2