Time Dilation: One 20-year-old twin brother takes a space trip with a speed of 0.80c for 30 years according to a clock on his spaceship. At the end of this trip, what are (a) his own age and (b) the age of his Earth-based twin brother?
A. (a) 20 y (b) 30 y
B. (a) 30 y (b) 50 y
C. (a) 50 y (b) 70 y
D. (a) 70 y (b) 90 y
Answer: C
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