F=M*A*A
True--but you're adding the charge of the horses, which could easily end up in a 60mph (100kph) collision. Nowadays we have seatbelts and airbags to handle that type of acceleration (and deceleration).
I doubt horses, with all that armor would go that fast.
Not sure if they wore armor in jousting contests, though.
Still, it is an important collision indeed.
