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Help needed for a force calculation

  1. May 8, 2015 #1

    I need to calculate the impact that a car (small car) has on a metal structure.

    What I know:
    The mass of the car : 99 kg, the velocity of the car : max 3 km / h -> 0,833333 m / s
    Thus the force of the car at 3 km / h is 82,5 newton.

    Now I need to know how much that metal structure can receive as impact.
    The structure is made of steel tubes with keyclamps. The tubes have a diameter of 42,4 mm and they weights 2.57 kg / m.
    The thing is that the structure is fasten in the ground with screws :p what doesn't make it easier to calculate I guess.

    I know it's a long shot, but if somebody could help me out how I can try to find something out to give a result ?
    The thing is I have learned all of these at high school but it's too long ago and can't remember :(

    Thanks for your help.

    Regards from Belgium
  2. jcsd
  3. May 8, 2015 #2


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    Science Advisor

    Sorry, that result is not even dimensionally correct. The product of mass and velocity has units of kilogram meters per second. That is a unit of momentum. The Newton has units of kilogram meters per second squared. It is a unit of force.

    However, you have another problem. Force, momentum, energy... None of them is a single magical number that equates to how much damage an impact will cause or how much a structure can absorb without permanent damage (though energy comes close). Collisions are complicated. Real world experience and experiment trumps high school physics calculations every time.
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