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Homework Help: Car bumper crash - deformation

  1. Oct 15, 2007 #1
    1. The problem statement, all variables and given/known data
    hi all,

    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?
  2. jcsd
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