Question

Why is it advised to tie any luggage kept on the roof of a bus with a rope

Answer 1

It is advised to tie any luggage kept on the roof of a bus with a rope because when the bus driver applies the break there is a chance for the luggage on the roof of a bus to fall down.

Answer 2

here is your answer dear....

It is advised to tie any luggage kept on the roof of a bus because when the bus stops suddenly then the bus comes in the state of rest but the luggage remain in the state of motion. so, due to inertia of motion, the luggage move forward and fall down from the roof of the bus.
If the bus starts suddenly, then bus comes in the state of motion but the remain in the state of rest. Due to inertia of rest, the luggage move in backward direction and fall down.

hope it helps you