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Question 19N.3.SL.TZ0.4c(ii)

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Date November 2019 Marks available [Maximum mark: 2] Reference code 19N.3.SL.TZ0.4c(ii)
Level SL Paper 3 Time zone TZ0
Command term Demonstrate Question number c(ii) Adapted from N/A
c(ii).
[Maximum mark: 2]
19N.3.SL.TZ0.4c(ii)

A train is moving across a bridge with a speed v = 0.40c. Observer A is at rest in the train. Observer B is at rest with respect to the bridge.

The length of the bridge LB according to observer B is 2.0 km.

According to observer B, two lamps at opposite ends of the bridge are turned on simultaneously as observer A crosses the bridge. Event X is the lamp at one end of the bridge turning on. Event Y is the lamp at the other end of the bridge turning on.

Events X and Y are shown on the spacetime diagram. The space and time axes of the reference frame for observer B are x and ct. The line labelled ct' is the worldline of observer A.

(c(ii))

Demonstrate using the diagram which lamp, according to observer A, was turned on first.

[2]

Markscheme

lines parallel to the x′ axis through X and Y intersecting the worldline ct′ at points shown ✔

so Y/lamp at the end of the bridge turned on first ✔

NOTE: Allow lines drawn without a ruler
Do not allow MP2 without supporting argument or correct diagram.

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