Understanding Wave Motion: Exploring the Path of a Point on a Wave

[bubakazouba]

Homework Statement

http://i1269.photobucket.com/albums/jj597/bubakazouba/114d22d10848ac93ac2fcea482ffe527_zpsedb41f24.jpg
the other line is a drawing of me trying to trace the wave(but of course its wrong,Im sry try to ignore it)
the answer is A

Homework Equations

My teacher told me that when we get a question like this to determine the point that I want to track its path and look at its left to see whether the point on its left is higher or lower than it
if it is lower then it will go downwards and vice versa.

The Attempt at a Solution

I tried that but it gets Q wrong, Q should get downward, why is it stationary?
which leads to the other question how can any point on the wave remain stationary after a time.

 

[tiny-tim]

hi bubakazouba!

each point can only move up or down (or be stationary)

to find which, look at where it was a moment ago, and where it will be in a moment's time

both times, Q is lower than it is now

 

[bubakazouba]

sorry i don't get it,
there are two instants {a moment ago, in a moment's time}
you said
"both times Q is lower than it is now", Q now is lower than Q now?