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Question 19M.3.SL.TZ2.bii

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.3.SL.TZ2.bii
Level SL Paper 3 Time zone TZ2
Command term Calculate Question number bii Adapted from N/A
bii.
[Maximum mark: 3]
19M.3.SL.TZ2.bii

A train of proper length 85 m moves with speed 0.60c relative to a stationary observer on a platform.

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.

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