SAT Subject Physics Practice Question 150: Answer and Explanation

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Question: 150

13. An astronaut lives on a spaceship that is moving at a speed of c away from the earth. As measured by a clock on the spaceship, the time interval between her maintenance checks on the ship’s main computer is 15 months. In the reference frame of the team here on Earth that monitors the ship’s progress, what is the time interval between maintenance checks on the ship’s main computer?

A. Always less than 15 months
B. Always exactly 15 months
C. Always more than 15 months
D. Initially less than 15 months, but after time more than 15 months
E. Initially more than 15 months, but after time less than 15 months

Correct Answer: C

Explanation:

Special relativity says that time dilates for objects moving at relativistic speeds, so the time should be greater (and never change). You could compute the exact value of the time as follows. If v = c, then the relativistic factor is

So, as measured by the team on the earth, the time interval between maintenance checks of the computer will be

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