Give an example showing that one and the same body can be considered a material point in one situation, but not in another.

A body is considered a material point when its dimensions are much less than the distance over which this body moves.

In this case, the size and shape of this body do not play a significant role and can be neglected.

When a train moves between cities, it can be considered a material point.

In a problem in which it is necessary to find the time for overtaking one train by another, trains cannot be considered a material point.

The stone falls from a certain height and it is necessary to find the fall time or the speed of the fall at the moment of impact. In this case, the stone can be considered a material point.

If in this task it is necessary to find the pressure of the stone at the moment of impact on the ground, then the stone cannot be considered a material point.