DP Physics (last assessment 2024)

Question 20N.3.SL.TZ0.b(ii)

Date	November 2020	Marks available	[Maximum mark: 3]	Reference code	20N.3.SL.TZ0.b(ii)
Level	SL	Paper	3	Time zone	TZ0
Command term	Determine	Question number	b(ii)	Adapted from	N/A

b(ii).

[Maximum mark: 3]

20N.3.SL.TZ0.b(ii)

The spacetime diagram is in the reference frame of an observer O on Earth. Observer O and spaceship A are at the origin of the spacetime diagram when time $t = t' = 0$ . The worldline for spaceship A is shown.

Event E is the emission of a flash of light. Observer O sees light from the flash when $t = 9$ years and calculates that event E is $4 ly$ away, in the positive $x$ direction.

Determine the time, according to spaceship A, when light from event E was observed on spaceship A.

[3]

Markscheme

light cone from E «crosses $c t$ at $9$ so» intersection on $c t' = 5.6 \pm 0.2$ $y$ «on $c t$ scale» ✓

$γ = 1.25$ ✓

so $t' = « \frac{5.6}{1.25} = » 4.5$ « $y$ after leaving Earth» ✓

MP1 accept use of linear equations to find $t = 5.625$

Allow ECF from (b)(i) and (a)

Examiners report

Those candidates who placed E at the correct position were then able to calculate the time appropriately.

Syllabus sections

Option A: Relativity

Option A: Relativity » Option A: Relativity (Core topics) » A.3 – Spacetime diagrams

Option A: Relativity » Option A: Relativity (Core topics)

Question 20N.3.SL.TZ0.b(ii)

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