Power plant producing electric power for relativistic trams says: Trams have large relativistic mass, that's why it takes lot of energy to accelerate a tram.


This is based on Doppler shift of EM-waves and momentum of said waves:


A tram moving away from the power plant says: I am not receiving much energy from those overhead AC-lines, the frequency is low and so is voltage. But the momentum of the energy is pushing me forwards with a small force.

A tram moving towards the power plant says: I am receiving lot of energy from those overhead AC-lines, the frequency is extra high and so is voltage. But the momentum of the energy is pushing me backwards with a large force.