Next question, question says of free 238 uranium nucleus, captain or train, amits an alpha particle. If the train is stationary a nucleus, decay and passenger measures at the separation between the alpha particle and the requiring nucleus becomes x at time t after the decay. If the decay takes place while the train is moving at a uniform velocity v or the distance between the alpha particle and requiring nucleus at a time t after the decay is measured by the passenger is option x plus vt x minus vt x or depend on the direction of the train. Now this is because in a national frame, one of your trains is on the rest, the second train is moving from your uniform velocity, so your x would be the right answer. So the scenario is that this is your train and uranium was here, the alpha particle was here and after time t distance is x, when there is rest, the same scenario will be your xe value, if your constant velocity is coming from the back, then same value will be here, if the acceleration will be there, in that case your non-inertial frame will be there, in that case your value will be different, but for this particular question, option c x would be the right answer.