Question

Will give pts! Please help :-(

An astronaut who is 30 years old gets into a spaceship and travels to the star 51 Pegasi, which is 50 light years away (this is the closest star to Earth that has a planet orbiting it). The spaceship quickly reaches its cruising speed of 0.9c. Ignoring the acceleration and deceleration at the beginning and end of the trip, how old does the astronaut appear to be when he reaches the new planet at 51 Pegasi? One light year is 9.46*10^15m.

The answer is apparently 43.4 years, but I need to know how to solve it :(

Answer 1

This seems to be a special relativity question. It looks like "time dilation" - time slows down at 0.9c and speeds of near that. I know of a book - "Special Relativity" by AP FRENCH of MIT which is fairly user friendly (not absolutely littered with grinding algebra and calculus).
Basically, something, from the astronaut in the example, to muons in French's book survive longer because they are travelling at the speeds you qoute. Time expands/slows down = dilation.
I'll have a look and see if there's an "easy" way of solving it.
If it is special relativity, you may need to find the formula for the Lorentz factor. It's in French, and probably elsewhere.
Bon voyage to Pegasi
http://perendis.webs.com

Answer 2

Agh thank you @osprey ! I did use the lorenz factor equation and kept getting an answer of 21.8, but apparently that's wrong...

Answer 3

21.8 times to is .. 43.6 ... there's "almost" a half missing somewhere ??? Whatever that last sentence actually means. Does it mean that you are half right ? What level of studying are you at - reason I ask is 'cos it can be difficult to glean from a question what the questioner's level of expertise is. If you know about the L factor equation, then you're doing a course in special relativity; at university ? This is a bit of a hobby horse of mine, and it might be nice to swap ideas ? I take it that you are familiar with Galilean (low speed) relativity ? Let me know, and bon voyage.

Answer 4

@osprey , I am studying at university! Physics course (my final is tomorrow lol). I'm just confused as to how to achieve that number D:

Answer 5

@kwonbon
What ? You're saying that your final exam is tomorrow ???? Hang on a tick. It's just starting september, so just starting term ... I thought that you did finals at the end of the year ??? What university.
He he, one of the things about this site is that I never know the level of the questioner. It would help to get a bit more help from them, but I can only dream. How are you on spherical harmonics and their use in electrostatic potential problems ?
Bon voyage encore.