Question

Free ${}^{238}U$ nuclei kept in a train emit alpha particles. When the train is stationary and a uranium nucleus decays, a passenger measures that the separation between the alpha particles and the recoiling nucleus becomes $x$, in $t$ time after the decay. If a decay takes places, when the train is moving at a uniform speed $v$, the distance between the alpha particle and the recoiling nucleus at a time $t$ after the decay, as measured by the passenger will be

• A. $x+vt$
• B. $x-vt$
• C. $x$
• D. depends on the directions of the train

Answer 1

Answer: (C)

$x$

Train is moving with constant velocity v.
There won't be any relative velocity change between alpha particle and uranium.
Hence, the distance will still be $x$.