IB · A · multiple choice
Space, time and motion · Question 6
Space, time and motion · Original GioPhysics question with a detailed, mark-by-mark answer guide.
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multiple choice1 mark
A spacecraft travels past Earth at 0.60c. A clock on board measures a time interval of 2.0 s between two events that occur at the same place on the spacecraft. What is the interval between those events as measured from Earth?
- A
1.2 s
- B
1.6 s
- C
2.5 s
- D
3.3 s
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Answer overviewCorrect answer: C — 2.5 s
01
1 markAnswer and reasoning
How to approach it
Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.
- 1
The correct choice is C: 2.5 s
- 2
A and B are shorter than the proper time, which no observer can measure — the proper time is always the shortest interval between two events, so the Earth reading must be larger. With γ = 1.25, the answer is 2.5 s.
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