A passing train*
A train with length 15 cs moves at speed 3c/5. (1 cs is one “light-second.” It equals (1)
(3 ⋅ 108 m/s)(1 s) = 3 ⋅ 108 m.) How much time does it take to pass a person standing on
the ground, as measured by that person? Solve this by working in the frame of the person,
and then again by working in the frame of the train.