Q86 · Practice questionComplex unfamiliar5 marks
QUESTION 86 (5 marks)
One twin remains on Earth while the other travels at to a star light-years away in the Earth frame and immediately returns at the same speed. Ignore acceleration duration. Determine the elapsed time for each twin and the age difference when they reunite.
WORKED SOLUTION
5 marksPractice marking scheme
ANSWER
Earth twin: ; travelling twin: ; age difference .
Worked solution
Earth-frame time for one leg is , so the round trip takes . At , . The traveller’s proper time is
Thus the travelling twin experiences less elapsed time. The turnaround means the travelling twin changes inertial frames, so the two full journeys are not symmetric.
Calculates one-way or round-trip Earth time.
Calculates gamma.
Calculates traveller proper time.
Calculates age difference.
Explains asymmetry due to frame change.
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