What is the increasing inertia of a 10,000 kg train at rest

No increase in inertia

Explanation:

According to law of inertia we know that if a body is at rest position it will remain in rest position and if a body is moving then it will remain moving until we apply any external force

Here it is given that the train is in rest means according to law of inertia it will be in rest until we apply any external force and its inertia will be constant

As its inertia is constant so there is no increase in inertia.

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.