Question

Any luggage kept on the roof of cars or buses is always tied with a rope. Why?

Answer 1

Any luggage kept on the of cars is always tied by a rope as when the car starts to gain velocity from rest, the luggage, due to inertia of rest, tries to retain it's original state of motion.

This causes the luggage to move backwards when the car moves forward.

Hence, luggage's are always tied to ropes.

Answer 2

because it experiences nertia of rest due to which it falls backward