DP Physics (last assessment 2024)

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

a(ii).

[Maximum mark: 2]

19N.3.SL.TZ0.4a(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 L_B according to observer B is 2.0 km.

(a(ii))

Calculate, for observer A, the time taken to cross the bridge.

[2]

Markscheme

ALTERNATIVE 1

time = $\frac{1.8 \times 10^{3}}{1.2 \times 10^{8}}$ ✔

1.5 × 10^–5«s» ✔

ALTERNATIVE 2

$t_{B} = \frac{2 \times 10^{3}}{1.2 \times 10^{8}} = 1.66 \times 10^{- 5}$ «s» ✔

$t_{A} = \frac{t_{B}}{γ} = 1.5 \times 10^{- 5}$ «s» ✔

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