Their combined momentum after they meet is 0 .
Products such as antifreeze are composed of organic compounds that are classified as <em>alcohols</em>. (a)
Maybe those other classes of chemicals also lower the freezing temperature of water, just like alcohol does. I don't know. But alcohol is what's used to make anti-freeze. I'm guessing alcohol must be cheaper, less toxic, and less corrosive inside the engines' cooling systems than any of that other stuff is.
Newtons 1st law of motion states that the object will continue to move at its present speed and direction until an outside force acts upon it.
So unless the objects inside the car are restrained, they will continue moving at whatever speed the car is traveling at, even if the car is stopped by a crash.
