Arock is held under water in a pond and is dropped from rest. while it sinks to the bottom of the pond, what happens to its motion? (more than one may be correct, so choose as many as are correct.)

select one or more:
a. the acceleration decreases.
b. the velocity increases and then decreases.
c. the velocity decreases and then increases.
d. the velocity of the rock decreases until it reaches terminal velocity.
e. the friction on the rock decreases as it approaches terminal velocity.
f. the acceleration of the rock in the water depends on its weight.
g. none of the above.

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.