Question

Why are passangers thrown in forward direction when running bus stops suddenly?

Answer 1

It's because of inertia. As the velocity of the moving bus is in the forward direction, our body is too moving along with the bus with the same velocity as that of the bus .But as brakes are applied the bus comes to an halt but our body continues moving in the direction of previously moving bus due to which the passengers are thrown forwards.
Think that helps

Answer 2

$\bf\huge\underline\mathbb\blue{ANSWER}$

When a moving vehicle stops suddenly, a passenger will tend to fall forward because the lower part of his body in contact with the seat comes to stop suddenly but the upper part of his body is still in motion sharing the movement of the bus. So on account of inertia, the passenger falls forward.