Little's law is another related phenomenon that is super critical. Measuring things when the units don't match has bitten me more than once.
Actually newtons are just a constant factor (3.6) compared to Wh per km, since there are 3600 seconds in a hour while there are 1000 watts in a kilowatt. For example 144 Wh/km (or 14.4 kWh/100 km) would simply be 518 N. This also means that pushing along a Tesla on the highway at constant speed is roughly as hard as holding a 50 kg weight, giving you an intuitive sense of how "hard" it is to keep things moving.
Of course, in everyday life, since we buy electricity from our utilities in kWh rather than joules, it's more convenient to talk about kWh per km (or per mile).
Actually, I guess the comment you replied to was also not really clear in it's point, so I'll blame that guy for maybe diverging from the topic somewhat :)
(not trying to be negative, really! but my brain is a bit fuzzy from being sick, so thus feeling a bit dimwitted as I ponder comments)