Using this block, a student wants to test a hypothesis that frictional forces are independent of the area of contact between the block and the surface it slides on. Which method is BEST to collect the data needed? D- Pulling the block across the same surface 10 times, adding a weight on top of the block each time.
A- Pulling the block across 10 different surfaces with the largest side in contact with them.
B- Pulling the block across the same surface with a different side in contact each time.
C- Pulling the block across three different surfaces with a different side in contact with each surface

the amount of current in the coil

-4 on

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.