In the evening you go back to the swimming pool with your friends. the object is still lying on the bottom of the pool in the same location as before, but since it's dark now, you use a flashlight to show it to your friends. remembering the apparent location of the object in daylight, where should you aim to illuminate the object with the flashlight? assume you hold the flashlight at eye level.
aim it above point, below point, or same location?

You should aim at an above point.

Explanation:

The light when it goes from the air to a densier substance as water suffers the effect called refraction in which the relative angle of incidence is different, in general, from the refracted one, as shown in the picture. Since water has greater density than air, then the refracted angle is smaller than the incident angle of the light beam, then to reach the actual location of the object from outside de pool it is necessary to aim a little above the real location, so that the light reaches it.

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.