Answer:
1.3734 years pass on the astronauts' clock.
The distance measured by astronauts is
![1.22*10^(16) \ m](https://img.qammunity.org/2020/formulas/physics/college/x3tmblqlt533ofblyjzqurckl7wnzqt55v.png)
Step-by-step explanation:
The fomula for time dilation is:
![t'=t\sqrt{1-(v^2)/(c^2) }](https://img.qammunity.org/2020/formulas/physics/college/zky8gfcp5q9e4t5jptapus0e7o171vxzmm.png)
where t' is the time observed by the astronauts, t is the time observed form Earth, v is the velocity of the astronaut and c is the velocity of light in a vacuum.
Replacing our values: t=4.2 year, v=0.945c
![t'=4.2\sqrt{1-\frac{{(0.945c)}^2}{c^2} } =\\\\=4.2√(1-0.8930 )=4.2*0.3270=1.3734\ years](https://img.qammunity.org/2020/formulas/physics/college/sl1vzcn4p9xi6gp5zrx3v1r6vbi675znxg.png)
The distance measured by astronauts will be their speed multolied by the time is takes them to get to alpha centauri:
![D=v*t'=0.945*c*1.3734=0.945*3.00*10^8 m/s*1.3734*3.154*10^7](https://img.qammunity.org/2020/formulas/physics/college/mc4674age6ar6goazowpnm03uyxyfwb8bi.png)
To acomodate fot units we write the speed of light in m/s and the amount of seconds in a year, so the resulting distance will be in meters.
![D=1.22*10^(16) \ m](https://img.qammunity.org/2020/formulas/physics/college/qsrfougtwv616c86iliicovzh9gxx217od.png)
We should compare this to the distance measured from Earth which is
![D=c*t=3.00*10^8 m/s*4.2*3.154*10^7=3.974*10^(16)\ m](https://img.qammunity.org/2020/formulas/physics/college/3r2jebn0zb2qn1ici9rkskaokspyd8bmdo.png)