How to write practice exams as a student as a way to study
One way to do it is to make a kind of game out of it. Instead of trying to write a complete exam, just come up with one question. Give it to your peers and expect an answer in a few minutes. The first to give a correct answer asks the next question. Each person will need at least a couple of questions to get started, but not a complete exam. Questions asked will, hopefully, help people think of additional questions. 

It would be good to do this face to face, but it could be done online if in real time - everyone simultaneously at their computer. 

If no one answers in the allotted time, the asker gives the answer and another question is asked, either by the same person or another. 

You might be able to use an online forum such as the physics section here to prime for questions. But searching for answers online sort of defeats the purpose of the exercise.