After some consideration I've come to the conclusion that it's very possible that the Mk2 suit could have sufficient weight to drop through a concrete floor and flatten a fibre-glass sport car body.
The original Iron Man Mk1 suit is described as being approximately 1500 pounds (over half a metric ton). The Mk2 isn't canonically weighed but there's a production quote from Shane Mahan (Head of Studio on Iron Man) stating that they were advised that the later suits would probably weigh something like 600-800 pounds or nearly a third of a metric ton.
600 to 800 pounds has always been the number that we kicked around
Assuming Tony's house conforms to Malibu Building codes then his floors are rated to a weight of 40 pounds per square foot. A suit that weighs something between 600-800 pounds would certainly fall outside the scope of this design standard and could very easily cause a structural failure including a "pancake effect" style floor collapse.
Similarly, a dead weight of half a ton hitting a sports car from a height of 10 feet would be more than enough to completely crush the bodywork.