Where are you, fellow enthusiasts?

One farmer was helping with the birth right next to the road that connects major cities. The birth was difficult; the calf was coming out backwards, not headfirst. So, the farmer grabbed the calf by its hind legs and pulled with all his might. The exhausted cow mooed in pain. A city dweller driving by saw all of this. He stopped and decided to help the farmer. In the end, they both managed to pull the calf out. Afterwards, they both went to wash their hands, and the farmer noticed that the city guy looked puzzled. Farmer: "Do you have a question?" City dweller: "Yes, I've been wondering for an hour: at what speed was the calf running before it crashed into the cow?"