I would not recommend Hempel for 31A, especially for anyone who did not take AP Calculus in high school.
The class has two midterms and a cumulative final. The first midterm had errors in two questions, one of which made the problem unsolvable. She kind of adjusted our grades, but her main solution was saying that we could have corrected the problem by changing one of the numbers and solved it like that (which almost no one did because of how the problem was written). The second midterm did not have any errors but was also quite difficult. The final was far easier than the midterms. I got an A on the final but the midterms brought me down to a B+. This was after having taken IB Math SL which my teacher taught the same as AP Calc. Hempel does allow cheat sheets on all the tests for equations you need to know.
In lecture, she would often start out concepts by showing the proofs, which took time away from learning how to do example problems. To me, the proofs were irrelevant for this math class because there were no proofs on the exams, and the lack of example problems make it much harder to do the homework and understand the material.
Homework is assigned, but you don't have to turn it in. I highly recommend doing the homework and also additional practice problems.
If you're a total math whiz, this class will probably be easy for you, but it may be challenging even for people who thought they were great at calculus in high school. I would really avoid this professor if you have no background in calculus.

This professor was one of the worst professors I have ever had. She made countless mistakes in lecture and for solutions! She was very unclear and super unhelpful.

Nadja Hempel has been to date the worst math professor I have ever learned from. She has a thick accent and to go along with that, she complicates the most basic math concepts. She doesn't have the competence to teach a class, her lectures are boring, and to top it off, she reads straight from the textbook. There was really no point in going to class. She messed up multiple times on the midterms she gave us and didn't want to own up to them so she still counted them for the grade. And the midterms were unnecessarily hard even my TA had trouble explaining some problems. Grading wise, she's a harsh grader. She has two different grading schemes for the class and she picks the one that's better for you but even that has its faults. The only way you can survive this class is if you are really smart with math or have a decent TA. If you have a choice, DO NOT TAKE HER. Otherwise, I wish you the best of luck

Although the Professor often made an effort to help and prepare us for exams, she usually still included questions on subjects that we did not go over. In many of her lectures, she would often get confused, causing the material to become unclear.

Avoid this class at all costs.
She rushes the material, cannot control the pace of the class, tests really harshly, and is very negative towards her students. I remember the last day in class she literally screamed she wouldn’t care if we gave her bad reviews on evaluations.
Well here’s a bad review: this was the worst class I’ve ever taken here, take it with another professor. I scored higher (A-) on 31B (a harder class) with a more difficult professor (midterm average 50)
I think the grade distribution tells all: it ruins your gpa for nothing.