Question

A girl runs a $100m$ dash. Her dad cheers for her as he watches.
According to the special theory of relativity (although the effects would be very slight) which of the following statements could be accurately stated (because of the effects of special relativity)?

• A. After the race, the dad could say to his daughter, "You were less massive during the race than you are now"
• B. After the race, the girl could say, "My time was a little better than I expected, but the race actually was not quite $100m$ long
• C. During the race, the girl could yell to here dad, "You are less massive now than you were before the race!"
• D. After the race, the dad could say to his daughter, "During the race, you were taller than you are now"
• E. During the race, the girl could yell to her dad, "You are shorter than you were before the race"

Answer 1

Answer: (B)

After the race, the girl could say, "My time was a little better than I expected, but the race actually was not quite $100m$ long

After the race, the girl could say, "My time was a little better than I expected, but the race actually was not quite 100m long, as Einstein's theory of special relativity states that the length of objects moving at relativistic speeds undergoes a contraction along the dimension of motion.