Helpful and organized.

Xu is the most helpful professor I have ever met, he is always open to students' questions. Most important, he is very brilliant and inspiring. As his convention, the first day lecture would mention the tensor which is the content should be learned in UD course, don't be scared, because his homework and exams are quite easier than you expect :)

Prof Xu is nice in person. Reply emails really fast. Yet exams are HARD. Homework not as hard, but some say it isn't close to exam questions. If you get extremely complicated expressions for your answer on exams, do trust yourself. The correct answers often look insane, and you should always attempt every problem cuz graders give partial credit.

Generally clear in the teaching. The class is very theoretical and focuses heavily on simplified models. Doing the homeworks made me very familiar with Mathematica too!

Prof. Xu is a good person. He is always patient in explaining the homework during office hours. His exams are challengeable but I think that will be beneficial to the students who are intended to pursue a career in physics.

Professor Xu is a very nice, caring, and smart person. However his teaching ability isn't really great. Instead of teaching us to understand how and why things were the way they were, we were given equations and simply expected to know how and when to use them. He is always open to questions but his explanations felt like a reiteration of the book

Prof. Xu is a very nice person. He spends time answering questions and helping with homework problems during office hours. However, I don't think he understands the general capabilities of the students in PHYS20. His homework and exams are way too difficult, given the way he teaches and prepares the students.

Pro. Xu is a nice person. He would even stop for 1 hour for unsolved problems. However, his lectures, exams, and homeworks are too hard. I have 3 AP Phy exams with scores of 4 but I can only get a 50 in midterm and final. (Average was about 60). If this course is not a p/np, my GPA will be doomed. PS, a solid foundation of calculus is important.

Talks really fast, a lot of homework (only 20+ questions, but each question takes me on average 20-30 mins, maybe others are different). I am a math major, but honestly, I think his class is really, really difficult. But he's a good guy, we can tell that he really wants us to learn and understand the materials. Curve is HUGE, midterm 60% is a B-

Xu is an interesting guy. Very kind when you go to office hours. Hard tests, be ready for conceptual tests.

I enjoyed this course. But one needs to know calculus really well in order to get a good grade.

Very interesting lectures! Dr. Xu is very kind and always willing to answer students' questions. Office hours are very helpful. But exams can be difficult.