* Velocity: This is a measure of how fast something is moving and in what direction. When a train is stopped suddenly, its velocity becomes zero.

* Acceleration: This is a measure of how quickly the velocity is changing. When the train is stopped suddenly, it experiences a large acceleration in the opposite direction of its original motion. Think of it as a big, sudden deceleration.

In summary:

* Velocity is zero when the train is stopped.

* Acceleration is NOT zero during the sudden stop, it's high (and negative).

Let me know if you'd like a more detailed explanation of acceleration!