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

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Discussion Overview

The discussion revolves around estimating the speed of a bus involved in an accident, based on the details provided by a participant. The scope includes practical applications of physics in accident analysis and the challenges associated with such estimations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • A participant seeks to estimate the speed of a bus that collided with their vehicle, providing details about the weights of both vehicles and the distance the car was propelled.
  • Some participants suggest that without skid marks, estimating the speed is virtually impossible.
  • One participant mentions that while it is possible to determine minimum braking distance using physics, the many variables and assumptions involved in a collision make it difficult to reach a useful conclusion.
  • Another participant recommends hiring a professional accident reconstructionist for accurate analysis and court testimony, emphasizing the limitations of informal calculations.

Areas of Agreement / Disagreement

Participants generally agree that estimating the speed without skid marks is highly problematic and that professional expertise is advisable for accurate assessments. However, there is no consensus on a specific method to estimate the speed based on the provided information.

Contextual Notes

The discussion highlights limitations such as the absence of skid marks, the need for experimental data, and the complexity of variables involved in vehicle collisions, which may affect the reliability of any estimations made.

stingle
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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!
 
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Welcome to PF!

stingle said:
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. …

Hi stingle! Welcome to PF! :smile:

Sorry, but without skid marks, it's virtually impossible even to estimate the speed. :redface:
 
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).
 
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.
 
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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