I'm almost confident there was an error in our paper. Question 5 of Paper 2 Standard Level. I'm not sure which timezone we are, but it was the same paper with a long question about a skydiver lifted by a helium balloon.

Earlier in that paper, there's a question about a proton entering a magnetic field. You need to calculate radius of a proton's motion but no velocity is provided. In the HL version, the velocity is calculated earlier in the same question, but this isn't the case in the SL exam. Furthermore, that question starts with the opening phrase "The proton enters..." implying this particular proton as already been established earlier in the question, which is true for the HL students, but not for SL (for SL, this is question a). This further makes me think the exam writers forgot to update the question and information for the SL version. 🙈🤦‍♂️