Aufgabe zur Relativitätstheorie

Question

Welche Antwort ist richtig?

Aufgabe:

A train is 200 feet long in its own frame, and a railroad platform is 160 feet long in its own frame. The train rushes past the platform so fast that, in the platforms´s frame, the train and platform are the  same length. How fast was the train moving?

- 4/5 c

- 5/4 c

- 3/5 c

-5/3 c 

Answer 1

Aloha :)$$\sqrt{1-\frac{v^2}{c^2}}\stackrel{!}{=}\frac{160}{200}=\frac{4}{5}$$$$1-\frac{v^2}{c^2}=\frac{16}{25}$$$$\frac{v^2}{c^2}=\frac{9}{25}$$$$v=\frac{3}{5}c$$