Circle root doesnt exist, atleast as far as i know. Square, cubic... exist.

Maybe its playing like for square - square root of 4 m2 = 200 cm. its square 2*2 m - surface area.

So if for circle you have surface area of pi m(i guess in this case it should write 2) - r2*pi=pi m so r2 =1 -- r= 1 m or 100 cm. But i dont know if thats solution. Or there is some word game in that ridle, because english isnt my native language, so i am not good in word games.

But for answer, we must wait creator of ridle.