1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Vehicle speed calculation from pedestrian throw distance

  1. Oct 25, 2016 #1
    How can we calculate the speed of a vehicle from pedestrian throw distance ?
    If the weight of a vehicle is 1220 kg and a pedestrian's weight is 72 kg. Throw distance is 20.70 meters.
     
  2. jcsd
  3. Oct 25, 2016 #2

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    Do you mean estimating how fast a car was going when it hit a pedestrian and threw them down the street? I'm not sure you can estimate that using only the information provided...
     
  4. Oct 25, 2016 #3
    Yes, that's what I want to know. What other information do you need ?
     
  5. Oct 25, 2016 #4

    Nugatory

    User Avatar

    Staff: Mentor

    To calculate using the laws of physics: the weight of the car, the weight of the pedestrian, the amount the speed of the car changed in the collision, the angle at which the pedestrian was thrown, the details of the damage done to the car in the collision including how much energy went into deforming fenders and the like, and probably some other stuff that I've overlooked.

    As you might conclude from this list, the answer to your question ("How can we calculate...?") is that we can't; it's not practical to calculate these things from first principles.
     
  6. Oct 25, 2016 #5

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    Another confounding factor would be that the pedestrian would typically not follow a projectile trajectory but rather slide on the road surface. You will have to read up on accident reconstruction analysis to really understand what current techniques look like.

    https://en.wikipedia.org/wiki/Traffic_collision_reconstruction
     
  7. Oct 25, 2016 #6
  8. Oct 26, 2016 #7

    Nugatory

    User Avatar

    Staff: Mentor

    The disclaimer at the McNally Associates website says pretty much the same thing - you can't calculate the answer you want.

    This thread is closed.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook