DP Physics (first assessment 2025)
Question 19M.2.HL.TZ2.6bii
Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.2.HL.TZ2.6bii |
Level | HL | Paper | 2 | Time zone | TZ2 |
Command term | Calculate | Question number | bii | Adapted from | N/A |
bii.
[Maximum mark: 3]
19M.2.HL.TZ2.6bii
(bii)
In the reference frame of the train a ball travels with speed 0.50c from the back to the front of the train, as the train passes the platform. Calculate the time taken for the ball to reach the front of the train in the reference frame of the platform.
[3]
Markscheme
ALTERNATIVE 1:
ALTERNATIVE 2:
v of ball is 0.846c for platform ✔
length of train is 68m for platform ✔
ALTERNATIVE 3:
Examiners report
Almost no candidates could use a Lorentz transformation to find the time of the ball’s travel in the frame of reference of the platform. Most just applied some form of t=γt’. Elapsed time and instantaneous time in different frames were easily confused. Candidates rarely mention which reference frame is used when making calculations, however this is crucial in relativity.

