DP Physics (last assessment 2024)
Question 19M.3.SL.TZ2.5c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.SL.TZ2.5c |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | c | Adapted from | N/A |
c.
[Maximum mark: 2]
19M.3.SL.TZ2.5c
Two protons are moving to the right with the same speed v with respect to an observer at rest in the laboratory frame.
(c)
Explain why there must be a resultant repulsive force on the protons in all reference frames.
[2]
Markscheme
there is a repulsive electric/electrostatic force «in both frames» ✔
the attractive magnetic force «in the lab frame» is smaller than the repulsive electric force ✔
in all frames the net force is repulsive as all must agree that protons move apart
OR
mention of the first postulate of relativity ✔
Examiners report
A few candidates mentioned that there was an electrostatic repulsive force between the protons in both frames. However very few realised that there had to be an overall repulsive force in both frames because of the relativity postulate.
