Why is it difficult to use the law of conservation of energy to calculate the
effects of a collision?

The law of conservation of energy is difficult to use for calculate the

effects of a collision because of  energy loss

Explanation:

We know that Collisions are of two types which is elastic and inelastic. The Law of Conservation of energy can be defined as in isolated system the total energy is said to remain constant and stays conserved over time can be applied on elastic collisions only as they don't lose energy and can not be applied on inelastic collisions due to energy  loss  in them due to heat and mechanical vibration. Hence, law of conservation of energy can not be used to calculate effects of collision

i believe the answer is a

russian is not my first language, so i'm afraid i can't write out an answer in russian, but hopefully you can find a way to do so. here's my best translation of the problem: you're given a plot of a particle's position in one-dimensional space over time, and you're asked to find either the total distance traveled by the particle after 6 seconds had elapsed, or the total displacement of the particle after 6 seconds.

if you want the total distance traveled, you would first need to determine the particle's velocity as a function of time, then integrate that over the 6-second interval. we know the position function is quadratic with roots at 0 and 6, so we have

where is unknown. because the position is parabolic, there is symmetry about the midpoint at , and we know that

so that the position function is

which means the velocity is

then the total distance traveled is

so the total distance traveled is 20 m.

on the other hand, if you want to find displacement: the particle starts at and ends at , so its displacement is 0.