i said "the carpet is found on the floor" - maybe a bit clumsy .... but is it incorrect?
Sort of... if I had to translate "They look for the carpet... the carpet is found on the floor", I can't think of any other way to say it. But when I see השטיח נמצא על הרצפה in Hebrew I understand נמצא as simply "is".
In this context, or lack thereof, I would understand the speaker simply to be identifying the location of the carpet, which reflects a static situation or stative idea. English has at least some (intransitive) uses of "[is] found" that closely approach this idea: "[such-and-such] is found [in such-and-such a place]". We could also use "[is] located" to express that an entity—at present time (or situation)—has a static, spatial position (i.e., situated [prototypically] somewhere in physical space in relation to other entities or things, such as, "on the floor"). Generally, as AlmogL suggested, English speakers would often just say that "[an entity] is [somewhere]" or that "[such-and-such] is [in such-and-such a place]".
The most important thing is to understand Hebrew-as-Hebrew: the actual meanings/ideas/conceptions that the language is used to convey in real communicative contexts and situations. Only then can we reasonably attempt to convey those same ideas in English. Grammar-translation methods can sometimes get us too focused on English translations rather than, or at least before, understanding the actual meanings conveyed by the language we're attempting to learn (similar to how children and native speakers learn their first languages, not having another language as a crutch to fall back on).
I noticed that the third definition in Wiktionary's entry for נמצא has "to be present, to be located, to be situated", which is what AlmogL was getting at.
Verb נִמְצָא • (nimtsá) (nif'al construction, active counterpart מָצָא)
to be found
to be discovered (clarification of this definition is being sought)
to be present, to be located, to be situated אתה נמצא כאן. ― You are here.
to turn out (become known or apparent)
It's not incorrect, but נמצאת sounds much more natural in hebrew than is found does in english. I would suggest ommitting it and saying simply "the carpet is on the floor."
At least in Hebrew there's a difference between רצפה (floor) which is inside a building and אדמה or קרקע (ground) which is outside (and usually unpaved).
Because the ground is typically referring to outside, where you wouldn't normally find a carpet, and because רצפה means floor not ground.