Question

Oscillation question,the answer is B,but what are the steps???
It looks pretty simple but I just can't get it right, in attached file, thanks in advance :)

Answer 1

Too bad the time line is not graduated with increments, it appears you will have to "estimate" what the particular time the two waves are separated by 1/8 cycle. One eighth cycle (1/8) is 45 degrees, so you are looking for a displacement of 45 degrees.
Here's what we know at 0 seconds P and Q are in phase, then at 18 seconds they are exactly 180 degrees out of phase. (P is at 90 Q is at 270 degrees)

Let's assume that the phase change is changing in a linear fashion, then at 9 seconds the difference would be 1/2 of that or 90 degrees, and that does seem to be the case, then we can further assume that 1/2 of that, 4.5 seconds, the difference is 45 degrees.

Answer 2

I believe this is a safe assumption, and examining the figure and laying a straight edge on my computer, and further estimating where 4.5 sec would be, it seems to bear this out.

Answer 3

This is more straightforward than that I believe.

Taking waveform Q it is 4.5 cycles to move from in phase to 180 out of phase.

i.e. 1.cycle out of phase.

You don not need to assume the linearity - the two waves have constant wavelength (each)

To be 1/8 out of phase will therefore take 1/4 of the time it takes to get 0.5 out of phase

= 18/4 = 4.5

Answer 4

Okay thanks for both your efforts ! I appreciate it although Idk why but those fractions just confuse me and the more questions I do the more confusing this gets :/
But I do get a point or two, so thanks a lot :)
@radar @MrNood

Answer 5

I believe to be 180 degrees out of phase, the two wave forms would 1/2 cycle out of phase not a complete cycle (360 degrees), I don't believe your 3rd and 4th line properly states that. @MrNood

Answer 6

You're welcome and good luck with your studies.

Answer 7

Can I get the formulas and basic concepts you used to get this conclusion?
So I do understand that 180 is exactly out of phase and that = 1 pi

Answer 8

Yes, that is what I have been taught also, for example if one wave is at 90 degrees (maximum positive) and the other wave is at 270 degrees (maximum negative) they are at that moment 180 degrees out of phase. Have a good day MonsterisEnergy.

Answer 9

That makes sense (:
Thanks a lot and have a nice day too.

Answer 10

yes - my third line should read
i.e. 1/2 cycle out of phase.