Question

Why does a passenger falls forward when a bus suddenly stops ?

Answer 1

This happens due to inertia of motion. Inertia of motion opposes any change in our state of motion so when the car, bus or any moving vehicle stops and comes to rest then we fall forward.

Answer 2

when the bus stops our legs is with the motion of the bus that is why it does not move forward but our upper body is still in the motion that is why it move forward.