The length of th train at rest is 471.4 m
Explanation:
Since the train is moving at a relativistic speed (=close to the speed of light), its length will appear contracted to an observer standing in the station, according to the equation:
[tex]L=L_0 \sqrt{1-\frac{v^2}{c^2}}[/tex]
where
L is the apparent length of the train, measured by the observer
[tex]L_0[/tex] is the proper length of the train at rest
v is the speed of the train
c is the speed of light
In this problem, we have:
v = 0.90c is the speed of the train
[tex]L=205.5 m[/tex] is the apparent length of the train
Solving for [tex]L_0[/tex], we find the length of the train at rest:
[tex]L_0 = \frac{L}{\sqrt{1-\frac{v^2}{c^2}}}=\frac{205.5}{\sqrt{1-\frac{(0.90c)^2}{c^2}}}=471.4 m[/tex]
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