Question

Answer the following.
1) Why is it advised to tie the luggage with a rope on the roof of buses?
2) Explain, why a glass pan of a window is shattered when a flying pebble hits it?

Answer 1

1) the luggage can fall off if it is not tied to the top of the bus

Answer 2

1) Due to inertia, when the bus stops/brakes then the luggage due it's inertia of motion tends to keep moving and thus falls off the roof.
2) Due to conservation of linear momentum. The pebble has some initial momentum and if it just stops after hitting the glass pane then this will imply \[m*u = m*0\] where m is the mass of the pebble and u is its initial velocity. Which is not possible. Therefore the glass pane needs to have some final momentum so that momentum is conserved.