A clock in a moving rocket is observed to run slow.
(a) If the rocket reverses direction, does the clock run slow, fast, or at its normal rate?
(b) Choose the best explanation from among the following:
I. The clock will run slow, just as before. The rate of the clock depends only on relative speed, not on direction of motion.
II. When the rocket reverses direction the rate of the clock reverses too, and this makes it run fast.
III. Reversing the direction of the rocket undoes the time dilation effect, and so the clock will now run at its normal rate?