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Can anyone help me figure out how fast a bus was going?

  1. Apr 30, 2009 #1
    I don’t know much about physics, but I was recently in an accident and I am trying to figure out approx how fast the other driver was going.
    What details would I need for the formula?

    I do know the object weighs 40,000 lbs (speed limit in area was 35, so I know it was going anywhere from 35-45 mph)
    I was hit with enough force to launch my car (weight 1800 lbs) 7-9 feet forward and rotate it over 180 degrees.

    There were no skid marks to measure the bus did stop approx 30 feet after impact.

    From the info above is there any way to figure out speed, if not what other info would be needed?

    I am not very good at numbers so any input/assistance would be greatly appreciated!
  2. jcsd
  3. Apr 30, 2009 #2


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    Welcome to PF!

    Hi stingle! Welcome to PF! :smile:

    Sorry, but without skid marks, it's virtually impossible even to estimate the speed. :redface:
  4. Apr 30, 2009 #3


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    It is possible using physics to determine minimum braking distance, given vehicle mass, velocity, and maximum braking force. However for a situation involving a vehicle collision, there are too many variables and too many assumptions which would have to be made to come to any kind of useful conclusion, let alone one that would stand up in court without experimental data. The best you could come up with would be limits of plausibility (e.g. if the bus driver claimed he only hit you at 2 mph you could prove this is physically impossible due to conservation of momentum).
  5. Apr 30, 2009 #4


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    Welcome to PF, Stingle.
    This subject has arisen before. The only practical approach is to hire a professional accident reconstructionist. Even if we could give you a formula (which we can't), you still need someone who can testify in court and be cross-examined. That is absolutely not in our job description.
  6. Apr 30, 2009 #5
    Thanks everyone, I figured as much, but I am not versed in laws of physics. I do appreciate you taking the time to help provide an answer.
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