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Date May 2018 Marks available 1 Reference code 18M.3.SL.TZ2.3
Level Standard level Paper Paper 3 Time zone Time zone 2
Command term Calculate Question number 3 Adapted from N/A

Question

Rocket A and rocket B are travelling in opposite directions from the Earth along the same straight line.

M18/4/PHYSI/SP3/ENG/TZ2/03

In the reference frame of the Earth, the speed of rocket A is 0.75c and the speed of rocket B is 0.50c.

Calculate, for the reference frame of rocket A, the speed of rocket B according to the Galilean transformation.

[1]
a.i.

Calculate, for the reference frame of rocket A, the speed of rocket B according to the Lorentz transformation.

[2]
a.ii.

Outline, with reference to special relativity, which of your calculations in (a) is more likely to be valid.

[1]
b.

Markscheme

1.25c

[1 mark]

a.i.

ALTERNATIVE 1

\(u' = \frac{{(0.50 + 0.75)}}{{1 + 0.5 \times 0.75}}c\)

0.91c

ALTERNATIVE 2

\(u' = \frac{{ - 0.50 - 0.75}}{{1 - ( - 0.5 \times 0.75)}}c\)

–0.91c

 

[2 marks]

a.ii.

nothing can travel faster than the speed of light (therefore (a)(ii) is the valid answer)

 

OWTTE

[1 mark]

b.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.

Syllabus sections

Option A: Relativity » Option A: Relativity (Core topics) » A.1 – The beginnings of relativity
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