This is because of tahe wind Resistance.mass of both things is same but the are of stone is small therefore it faces less wind resistance but in case of feathers the are is distributed in a larger are than stone so the stone falls faster than feather in normal condition but when there is vacuume the wind resiatance is 0 then due to the effect of gravity they both will fall at same speed .Hope u understood this .If it wass helpful plz mark it the brainliest