You will have maximum force here, maximum force, maximum force like this. So, the force variation will be like this, let me say that the wave is moving in this direction. So, if I have, if I need to get the total force, then I have to integrate this total force. So, I instead of picking it from the figure, we can also evaluate the phase at which the maximum force occurs. And that is what we have done earlier in the lecture material; please go through the lecture material. So, you will understand how this theta max is determined. So, this problem clearly conveys to us, the phase variation of the wave force, and how what kind of information we can obtain. Thanks.