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The identical twins Speedo and Goslo join a migration from theEarth to Planet X.

ID: 1748100 • Letter: T

Question

The identical twins Speedo and Goslo join a migration from theEarth to Planet X. It is 24.0 ly away in areference frame in which both planets are at rest. The twins, ofthe same age, depart at the same time on different spacecraft.Speedo's craft travels steadily at 0.970c, and Goslo's travels at0.750c. Calculate the age difference between the twinsafter Goslo's spacecraft lands on Planet X. (Goslo is the oldesttwin)

I know that a similar question is answered in Chapter 39 problem 14but I don't understand that work, I think a few steps might bemissing from that one or something. Anyway, can someone help me outwith this one? What formula do I use, what do I about the lightyears? Any help would be appreciated!!!


Explanation / Answer

Let the distance to planet X be S
Given S=24 light years

           =24 * 3x108 * 1 year

time taken for speedo's craft t= S/v

                                           = ( 24 * 3x108 * 1 year) / 0.970 c

                                           = [24/0.97] 1 year    Since c =3x108 m /s              ------( 1)

time taken for goslo,s craft t ' = S /v '

                                             = ( 24* 3x108 * 1 year)/ 0.750 c

                                             = [24 / 0.75 ] 1year                -----( 2)

relative time of Speedo's T = t ( 1 -(v/c)2)

                                          = t ( 1 - (0.97c/c)2)

                                          = 0.243 t

                                          =  6 * 1year             Since from eq ( 1)
relative time of Goslo's T ' = t ' ( 1 - (v '/c)2)

                                       = t ' ( 1 - (0.75c/c)2)

                                     = 0.6614 t '

                                     = 21.16 * 1year             Since from eq ( 2 )

Correction for "after Goslo's spacecraft lands on Planet X."

Since Speedo gets there in t01= S/v1= [24/0.97]Y he has to wait for Goslo to arrive.

Speedo' age will be equal to A + 6 years + waitfor Goslo time t' or

t' = t01 - t02 | =[24/0.75]Y - [24/0.97]Y = 7.2577Y

Speedo' age = A + 6Y + 7.2577Y= A + 13.2577Y

Goslo's age = A + 21.16Y

Their age difference is A + 21.16Y   - (A+ 13.2577Y) = 7.9 Y