When a speeding bus stop suddenly, passengers are thrown forward from their seats because

Options

A. the back of seat suddenly puushes the passengers forward.
B. inertia of rest stops the bus and takes the body forward.
C. upper part of the body continues to be in the state of motion whereas the lower part of the body in contact with seat remains at crest.
D. upper part of the body come to resst whereas the lower part of the body in contact with seat begins to move.

Explanation

### Step-by-Step Solution:

1. **Understanding Inertia**: Inertia is the property of an object to resist changes in its state of motion. An object in motion will continue to move at a constant velocity unless acted upon by an external force.

2. **Situation Analysis**: When a bus is moving at high speed, both the bus and the passengers inside it are in motion. The passengers have a certain velocity in the direction of the bus's movement.

3. **Sudden Stop of the Bus**: When the bus suddenly stops, the lower part of the passengers' bodies, which are in contact with the seat, decelerates and comes to a stop due to the friction between the seat and the passengers.

4. **Upper Body Motion**: However, the upper part of the passengers' bodies does not immediately stop because it is not in contact with the seat. According to the principle of inertia, the upper body continues to move forward at the same speed the bus was traveling before it stopped.

5. **Resulting Motion**: As the bus stops, the back of the seat exerts a force on the passengers' upper bodies. This force acts as a sudden deceleration for the upper body, causing the passengers to be thrown forward relative to the bus.

6. **Conclusion**: Therefore, passengers are thrown forward when a speeding bus stops suddenly due to the inertia of their upper bodies, which continue moving forward while the lower bodies come to a stop.