00:01
Let's go ahead and copy down that wave function.
00:03
Y of xt is equal to 0 .35 meters times the sign of 1 .25 radiance per meter times x minus, excuse me, plus 99 .6 radiance per second times t.
01:03
Great.
01:05
So now we're going to consider the element of the string at x equals 0.
01:10
And we want to know what is the time interval between the first two instance when this element has a position of...
01:17
So we're going to just substitute in x equals 0 and y equals 0 .175 meters.
01:37
0 .175 meters, right? we're going to use that equation right there to solve for t.
01:45
And now because this is a sign function, we should have actually infinitely many...
01:52
Points in time that this occurs, right? so let's just go ahead to fill those numbers in.
02:17
I'm going to ignore units just for now just to save some space.
02:24
This is being multiplied by zero, so i won't even write that in there.
02:30
99 .6.
02:34
99 .6 times t, right? yeah, so i mean, let's just divide by 0 .35 .0 .0.
02:58
0 .175 by 0 .35 .05.
03:06
0 .5 is sign of 99 .6 t.
03:16
We can take the arc sign of this and see what we get.
03:26
So 99 .6t is equal to the arc sign of 0 .5.
03:33
Yeah, so i mean the arc sign of 0 .5, that's like at which angles is the sign equals to 0 .5? well, at this occurs at, i think it's pi over 6.
03:58
Yeah.
04:00
So i think we got pi over 6.
04:01
So 99 .6t is pi over 6.
04:07
And it also occurs on the other side of the unit circle, which, let's see, so we got pi over six, then pi over four, then pi over three, and then pi, or no, yeah, pi, pi for two.
04:31
And then we got, i think it's, i think it should be, so that's three pi over six, right? so then we got four pi over six, right? and that not there, but keep going.
04:45
4 pi over 6.
04:46
Then we got, i think it should be 2 pi over 3, right? or maybe it's 5 pi over 6, 5 pi over 6.
05:04
5 pi over 6, i think.
05:12
Let me use a calculator just to be sure.
05:14
Because i'm doing the unit circle in my head right now.
05:17
Yeah, those two are the correct angles.
05:20
So now we will just take our, now we'll just solve for the t's.
05:24
The two time intervals here.
05:27
Pi over six, that's going to be over 99 .6 times six.
05:35
And this one will be 5 pi over 99 .6 times six...