Question

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

Answer 1

Hint
You are advised to tie any luggage kept on the roof of a bus because when the bus accelerates or decelerates, in simple words, when the bus starts from the rest or brakes are suddenly applied, any unsecured or untied luggage might fall off the roof. To know why this happens, you need to be aware of the concept of moment of inertia.

Complete step by step answer
We all are aware of the fact that mass is an inherent property of matter; every object having mass possesses some moment of inertia. It is a property which helps the body to oppose any changes in its state, be it of rest or uniform motion. To further explain inertia, we can say that any object moving with uniform speed tends to keep doing that until an external force is applied to it. When the luggage is kept on the roof of a bus, it keeps moving with the bus, and suddenly if the driver applies the brakes, the bus will come to stop but the luggage will try to maintain its state of motion and might fall off the roof.
A similar observation can be made if the bus is at rest and then the driver suddenly presses on the accelerator. The bus will move forward but the luggage will try to remain at rest and will also have great chances of falling off.
This problem can be avoided by tying the luggage with the help of a rope.

Note
It should be noted that even though the luggage tends to fall off whether the bus comes to a sudden stop or whether it starts sudden acceleration. If the bus suddenly stops, the luggage will fall in front of the bus. On the other hand, if the bus suddenly starts from rest, the luggage will fall behind the bus.