Question

if a stone and a feather trown at a same velocity who will reach first

Answer 1

Any object thrown horizontally or vertical or at angle to horizontal with the same velocity V will reach the destination on ground in the same time. the time duration depends on the V and angle at which it is thrown and the height from which it is thrown.

So a feather and a stone thrown with Velocity V from same height will reach the ground or target at the same time.  This is the ideal case, when there is no air and it is all vacuum. Any of object of any density should reach in the same time.

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When there is air around, the objects lose weight according to Pascals' law. There is buoyancy force acting on feather and stone opposite to the direction of travel. Buoyancy force is more on the feather than the stone, because the density of feather is less than that of stone. So the feather floats in air longer and reaches slowly. Stone faces less buoyancy force from air, so it reaches fast.