Answer:
Newtons 1st Law states that any object in motion will continue to move in the same direction and speed unless forces act on it. So, since the objects in the bus are moving forward (because the bus is moving forward), they'll continue to go forward when the bus stops, until something like gravity or a bus seat stops them moving.
They'll move backwards at the sudden speed, as they had 0 Newtons of force acting in either direction, so it won't move straight away until there's a higher net force in once direction (net force being how much force is acting on one side of and object compared to another, so say 5N forwards and 3N backwards on an object, would have a net force of 2N)
