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.
It depends on the angle and speed of the entry as well as the composition of the rock whether it burns up or not. And rocks that small are not listed as threats - again the likelihood of hitting a city are vanishingly small - Chelyabinsk got lucky.