# Vehicle speed calculation from pedestrian throw distance

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.

Mech_Engineer
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...

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...
Yes, that's what I want to know. What other information do you need ?

Nugatory
Mentor
Yes, that's what I want to know. What other information do you need ?
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.

Mech_Engineer
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

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