0:00
16 .70.
00:01
So we've got the transverse acceleration plotted here for some wave on a string as a function of time at the x equals zero point on it.
00:15
And we're told that this has the form of an amplitude times the sign of kx minus omega t plus phi, which i forgot to write the whole point of the problem in here.
00:31
And then the scale of this is set by 400 meters per second is what a sub s is.
00:38
So the function that's plotted here, we just set x equal to zero.
00:44
And now this is the acceleration.
00:46
So we need to take two derivatives of this.
00:51
So we're going to get a negative omega out two times from just the chain rule.
01:02
And then we're going to get an additional negative.
01:05
Sign from the differentiating the cosine of the speed into the velocity into the sign again of the acceleration.
01:17
So we end up with a negative sign and you can work through that out yourself if like a quick little verbal explanation of what we're doing is a little difficult to follow.
01:33
So x is zero, so this is just negative omega t plus phi.
01:43
So now at time zero, this is negative.
01:48
I'm sorry, the slope is negative...