Question

why does a bucket of water weighs less inside the well water

Answer 1

When a bucket of water is put inside te well, then a buoyant force which is equal to the weight of the object acts on it thus making it weigh less..

Answer 2

the bucket of water weighs less inside the well because of the buoyant force acting on the bucket buy on force is a force When an object is placed in a fluid, the fluid exerts an upward force  due to this it weights less in water