Question

A van came around a corner a hit me as I gently pulled off in a small car to help my court case we measure I was pushed over 40 meters How can I give an idea as to how fast he must have been travelling? Unfortunetly it is on the Isle of Man on a no speed limit road however it is to prove that I stopped and checked and had no chacne of him hitting me with the speed in which he was travelling? Thank you