Question

Usain Bolt is capable of running a 100 m dash race in 9.58 s, or about 23.4 mph. Suppose you are traveling in space during the race and moving at 90% the speed of light. What average speed to you observe Bolt to run the race at, in mph?

In the previous problem, the observers on Earth and on the spaceship measure two different speeds, so who is right? Bolt can’t be running at two different speeds at the same time can he? Explain your answer conceptually in terms of relativity.

Answer 1

Both the observer on the earth as well as on the spaceship is right , because both of them are measuring the speeds in their own frame of references and we know that speed is a relative quantity and it varies with the chosen frame of reference.

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