DP Physics (first assessment 2025)

Question SPM.2.HL.TZ0.2

Date	May Specimen-2023	Marks available	[Maximum mark: 6]	Reference code	SPM.2.HL.TZ0.2
Level	HL	Paper	2	Time zone	TZ0
Command term	Calculate, Determine	Question number	2	Adapted from	N/A

[Maximum mark: 6]

SPM.2.HL.TZ0.2

A spacecraft is flying past a space station at a relative speed of 0.80c. Beacons, R and F, at each end of the space station emit light pulses at the same time according to observers on the space station. The pulses are emitted 1200 m apart as measured by space station observers.

(a)

Calculate $γ$ for a speed of 0.80c.

[1]

Markscheme

$γ = \frac{1}{1 - 0 . 80^{2}} = \frac{5}{3} = 1.67$ ✓

(b)

Calculate, for the reference frame of the spacecraft,

(b.i)

the distance between the light pulses.

[1]

Markscheme

« $Δ x' = γ (Δ x - v Δ t) =$ » $\frac{5}{3} \times 1200 = 2000$ «m»

Allow ecf from 1a.

Allow use of $L = \frac{L_{0}}{γ}$ .

(b.ii)

the time between the light pulses.

[2]

Markscheme

« $Δ t' = γ (Δ t - \frac{v}{c^{2}} Δ x) =$ » $\frac{5}{3} (0 - \frac{0.80}{3 \times 10^{8}} \times 1200)$ ✓

Δt'«−»5.3 «μs» ✓

Allow use of $Δ t = γ Δ t_{0}$ .

(c)

Determine which light pulse happened first.

[2]

Markscheme

Because $Δ t' < 0$ ✓

F occurred first ✓

2^nd MP only awarded if correct interpretation of 1^st MP.

Syllabus sections

A. Space, time and motion

A. Space, time and motion » A.5 Galilean and special relativity

Question SPM.2.HL.TZ0.2

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