Except that much of it would burn up on entry making the resulting rock far smaller and unlikely to hit a city - open ocean water more likely that some city - most rocks never make it to the surface, only worry if if is one mile or more in size.
Don't be absurd. Anything rock bigger than about a city bus will not burn up entirely. A 400 foot object would be through the entire atmosphere in something like 3 seconds with over 99% of its mass.