# Question about the Lorentz factor

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## Summary:

A rookie physics fan

## Main Question or Discussion Point

Brief intro: I'm awful at maths and really interested in physics.

My friend asked me to solve a question but I can't seem to wrap my head around it...

The question: If I'm listening to a song that lasts 5 minutes and 30 seconds and my twin brother travels to the moon and back while the song played aged 4 minutes and 38 seconds in that time what was my brothers average speed?

## Answers and Replies

It's about a 768800 km round trip, accomplished in 278 seconds, so simple division says he moves at an average of about 2765 km/sec, nowhere near enough speed to experience any relativistic time dilation, at least not in a problem done in 3-4 digits of precision. The most pressing question is how far away the moon was the day he did this.

Apparently the round trip took place in less time than it took for the song to play.

EqualsMC2
It's about a 768800 km round trip, accomplished in 278 seconds, so simple division says he moves at an average of about 2765 km/sec, nowhere near enough speed to experience any relativistic time dilation, at least not in a problem done in 3-4 digits of precision. The most pressing question is how far away the moon was the day he did this.

Apparently the round trip took place in less time than it took for the song to play.
Wow thank you!

mfb
Mentor
Your brother could travel to the Moon and back many times. His average speed would depend on the way he does so. A constant speed will lead to a different average than "zero for 4:37 and then nearly the speed of light for the rest of the time".