00:01
In this problem, we're looking at two pulses in a slightly different way.
00:10
So in a, we're just asked, how do you get from figure a to figure b, how many seconds? so i see that the triangle that's on the right side starts at 7 meters and goes to 9 meters.
00:49
And it's moving to the left.
00:57
I need to move it until it reaches three.
01:04
It used to be at seven, and i want it to go the whole way to three.
01:11
And so, if they're moving at one meter per second, it started at seven, and it wants to go, one it to go to three, seven minus three is four.
01:24
So, t equals four seconds.
01:30
So what i'm going to do is i'm going to now verify that i'm correct by draw.
01:36
This at four seconds.
01:44
So this is one here.
01:50
T equals four seconds.
01:54
So in four seconds, the one on the left, which i'm going to make red, is going to go over to four.
02:03
So let me just put some tick marks on here.
02:09
One, two, three, four, five, six, seven, eight, nine.
02:16
Okay.
02:17
The one on the left goes over to four.
02:21
And so what it would look like then is four to five.
02:27
And then its width is two at the top to seven.
02:35
All right.
02:38
The one on the right is green.
02:43
It used to start at 7.
02:46
7 minus 4 is 3.
02:49
So it's going to go from here up and down.
02:57
So when you add these together, i'm going to make the blue line, the addition of the two.
03:07
Right here where they overlap, one half plus one half is one.
03:15
And we see that at every point they're going to add up.
03:18
To one.
03:20
And so that does give us the shape from three to seven that we see in figure b.
03:29
So let's go on to part b of this question.
03:36
We need a history graph of the string at x equals five.
03:50
So displacement in centimeters x equals five.
03:59
Well, from t equals 0 to t equals 6.
04:04
So 0, 1, 2, 3, 4, 5, 6.
04:10
1, 2, 3, 5, 6, and this is time in seconds.
04:20
Okay, at time 0, which is the first graph, figure a, at 5, we see nothing.
04:32
So the height of the blue wave is nothing.
04:36
At t equals one, they both move one closer to each other.
04:41
So the left one is going to move to four...