Final answer:
When analyzing collisions, it is easier to analyze an elastic collision. The criterion for determining Eulerian or Lagrangian viewpoint is based on the frame of reference.
Step-by-step explanation:
In the context of analyzing collisions, it is generally easier to analyze an elastic collision compared to an inelastic collision. In an elastic collision, kinetic energy and momentum are conserved, which makes it easier to calculate the final velocities of the objects involved. In an inelastic collision, kinetic energy is not conserved, which introduces additional variables.
When determining the viewpoint as Eulerian or Lagrangian, the criterion for making this determination is based on the frame of reference. In Eulerian viewpoint, the observer looks at the system from a fixed point in space, while in Lagrangian viewpoint, the observer looks at the system from the perspective of one of the objects in the system. The choice of viewpoint depends on which perspective is more convenient for solving the problem at hand.