which of the following objects - airplane, L train, person - would be easiest to model the motion of? Which would be the most difficult?

motion of transportation and a person would be the most difficult

Model the motion of a train would be the easiest. Model the motion of an airplane would be the easiest.

Explanation:

The advantages in modelling the motion of a train is that it goes on a rail with constant velocity most of the time, in a predictable direction.

On the other hand, an airplane is much more difficult because fluid dynamics (the interaction between air and the plane) has to be considered