A bird is at rest on the floor of an air tight box which is being carried by a boy. If the bird starts flying, he feels the box as:      

A bird is initially at rest on the floor of an air tight box which is being carried by a boy is felt to be having certain weight.

As bird start flying by pushing air to avail up thrust equal to its weight then also boy feels the box to be having same weight as before because same thrust will result on base also.