Question

what happens if the luggage placed on roof of a bus not protected with rope

Answer 1

if the luggage placed on roof of a bus not protected with rope thier is a chance that the luggage will fall down when break will be applied

Answer 2

If the luggage placed on the roof of a bus not protected with a rope then it will fall because according to newton's law of inertia when the bus moves, the luggage will also in motion but when the bus stops the luggage will tend to remain in inertia of motion (or just motion ) and ultimately fall.