All of my friends say that if a car made of mostly carbon fiber would crash into a full steel car, or vice versa, the steel car would be DESTROYED and the carbon fiber would drive away, if not, easily repairable.
Ok, your friend is wrong. Carbon fiber can outperform steel in many applications. It is lighter and stronger in tension. Compression, however, is not a property carbon fiber composites do well under. The strength of carbon fiber composites comes from the design, or layup, of the fibers. When the layers are properly orientated the composite can do very well. But, it can’t handle stress from any direction, only the directions it’s designed to be used in. Now, back to the car crash… A crash is a situation involving high amounts of crushing forces and shockwaves that would travel around the vehicle. If the impact itself didn’t crush the composite, the shock waves could cause hidden damage, such as delimitation, in areas that may not even be close to the impact area. As for it being easy to fix, well that is also dead wrong. Unlike steel, carbon fiber composites can’t be welded, straightened, or bent into place. Once a composite has sustained damage it usually needs to be replaced. Closing thoughts… Keep this in mind, it’s not the fibers themselves that are so weak, it’s the glue holding them together. As of today, the only way to make these strong light weight components is to glue them together. They do a good job doing what they are designed to do, but fail easily with impact and compression loading.
Depends on the design/construction.
At a reasonably high speed, both cars would be undrivable. That's by design, not due to the strength/weakness of the materials. The energy in an impact needs to go somewhere. Cars are designed so the body and the frame will bend and break, reducing the impact on the occupants. If the car is too rigid the chances of the occupants being injured increases. Carbon fiber composites do have a better strength to weight ratio than steel but they're also a lot less dense, so the same volume of material will have a similar strength. The primary benefit to carbon fiber is that for a part of the same strength the carbon fiber part will weigh less than the steel part.
