Question

If a stationary bus suddently speeds up, passenger are thrown in the baclward direction.

Answer 1

that is nothing but centipetal force acting .

you will see when a car turn rights body moves towards left same will happen when bus start going forward the body moves backwards

Answer 2

<b>This is Newton's laws of motion in play.

When the bus moves, your body due to inertia tends ito remain in the same position. So you feel the backward motion. Similarly when the bus stops, your body( part of it which is free to move) continues to move and you tend to lurch forward.