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Calculate vehicle speed based on impact results?

  1. Jan 17, 2012 #1
    I hope I'm not asking too much.

    Other Driver hit Family Member. I want to calculate how fast OD was going. Desired results would be accurate to within 5 MPH or less.

    OD was in a 2003 Hyundai Elantra; googled curb weight around 2700.
    FM was in a 2005 Nissan Titan; googled curb weight around 5000.
    Impact was on passenger side rear axle of the Titan.

    Titan was spun approximately 180 degrees and passenger side was lifted off the ground. I'm don't have specifics on that yet, such as did the curb stop the spin and therefore cause the truck to start a rollover, or did the impact generate the lift and the spin came to a "natural" stop? Police report indicates the Hyundai scraped the road, causing damage to the street surface. I don't have more specific info than that.

    Dry asphalt. Almanac.com provided the following temps on the day in question:
    37.4 °F

    41.4 °F

    48.2 °F

    The accident occurred on a March afternoon in a northern latitude an hour prior to sunset, so temps should not have fallen too much.

    I'm sure more info is needed but I don't know enough to know what that is. Any help appreciated.
  2. jcsd
  3. Jan 17, 2012 #2


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    Accident investigations are very complicated. Energy is lost to deformation of the cars. Momentum is lost unless you include the relatively tiny effects on the relatively massive earth. How much energy is consumed by the brakes and tires depends on how much braking was involved and how much sideways sliding was involved.
  4. Jan 17, 2012 #3
    Thanks for the reply.

    No braking was involved. The only sliding that I'm aware of is the arced motion of the rear truck wheels.

    What other info should I gather? Or is there simply too much?
  5. Jan 18, 2012 #4


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    There are a lot of details involved. Weight distrubtion of the vehicles, coefficient of friction for the tires, did the tires hop or did other body parts of the car scrape the ground which would affect friction coefficient. I'm not sure how suspension plays a roll in the reaction to a collision. How much deformation occurred, ...
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