#### Answer

When the train is at rest, Emma is at rest on the train, As the train starts to move forward, Emma's inertia keeps her at rest initially. There is no thrust toward the rear of the train.
When the train is moving at a constant speed, Emma also moves at a constant speed with the train. As the train first starts to decelerate, Emma's inertia keeps her moving forward at a constant speed. There is no thrust forward.

#### Work Step by Step

When the train is at rest, Emma is at rest on the train, As the train starts to move forward, Emma's inertia keeps her at rest initially. There is no thrust toward the rear of the train. Instead, Emma stays at rest momentarily as the train accelerates forward, which gives the feeling of receiving a thrust toward the rear of the train.
When the train is moving at a constant speed, Emma also moves at a constant speed with the train. As the train first starts to decelerate, Emma's inertia keeps her moving forward at a constant speed. There is no thrust forward. Instead, Emma's inertia carries her forward at a constant speed which gives the feeling of a thrust forward relative to the decelerating train.