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How to calculate the speed of a vehicle on impact

  1. May 8, 2012 #1
    A friend posed this question to me tonight.

    If a vehicle hits a stationary object and you know the distance travelled of the object, the weight of the object, the model of the vehicle and that conditions were dry on a tarmac road, is it possible to work out the speed of the vehicle on impact?
     
  2. jcsd
  3. May 8, 2012 #2
    280 views and no reply?? Is it possible to calculate?
     
  4. May 8, 2012 #3

    HallsofIvy

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    What, no answer in all of an hour and half? There simply isn't enough (and most of what you listed, the model of the vehicle, the condition of the road,etc., is not relevant). Even assuming a "perfectly elastic" impact, you would need to know, for example, how the impact affected the speed of the vehicle- so you could calculate the exchange of energy.
     
  5. May 8, 2012 #4
    Sorry mate. Was just trying to help out a friend who had property damaged in an RTC. Was just asking if it was possible to get a calculation of whether the vehicle was travelling over the 30Mph limit when it hit his property.
     
  6. May 9, 2012 #5

    haruspex

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    The key problem is knowing what would have limited the distance travelled.
    If the object is a ball on a hard level surface, it could travel 100s of metres without too much encouragement.
    If, at the other extreme, it was a dead weight that would not be likely to slide or bounce very far then you can put a lower limit on the speed.
    Of course, if there is forensic evidence to show where the object first hit the ground, as a distance from the impact location, that will do instead.
    The greatest distance for a given speed would correspond to the object's having been launched at 45 degrees to the horizontal. The distance will also be greater if the object had a higher centre of gravity when struck than when it landed.
    Can you fill in some of these details?
     
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