(True/False): It is possible to detect the approaching of a distant train by placing the ear very close to the railway line.

How is it possible to detect the approaching of a distant train by placing the ear very close to the railway line ?

It is possible to detect a distant train, which still can't be heard, approaching us by placing our ear very near to the railway line. How this works ?

Lenses Placed Very Close To Each Other

Would it be possible to detect on Earth sounds produced on another planet if you had a dector sensitive enough to very low intensity sounds ?

It is possible to add n vectors of equal magnitude and get zero: (True , (b) False