# Car bumper crash - deformation

1. Oct 15, 2007

### brokenlickz

1. The problem statement, all variables and given/known data
hi all,

Given:
a car is reversing at 4km/h, weight = 1500kg... n whamps into a lamp post. i'm suppose to calculate the bending of the bumper, which is made of AlZn4,5Mg1 material.

bumper is 900mm long n fix onto the car body
dimension : 80x80mm U profile with a 5mm thickness

2. Relevant equations

3. The attempt at a solution

i assume that we should use the kinetic energy formula which is

E = 1/2mv2

to get the amount of initial energy.

According to the law of conservation energy.

initial energy = final energy
= deformation energy/potential energy + sound energy(neglegible) + heat (neglegible )

from my what i've considered here, i guess i need a force F in order to calculate the bending distance of the bumper.

but from the formulas i have above, how do i go about getting the force F which works on the bumper?

the area underneath the stress strain diagramme of this material wouldnt help much because i couldnt really calculate (accurately) the area after the elasticity limit right?