It largely depends on how easy it is to get the energy out all at once. A stick of butter represents about 1kWh of chemical energy, and a 2000kg vehicle at 225

It largely depends on how easy it is to get the energy out all at once. A stick of butter represents about 1kWh of chemical energy, and a 2000kg vehicle at 225 km/hr represents about 1kWh of kinetic energy. The latter is intuitively more dangerous because the energy could easily be transferred (to e.g. a person standing in its path) in an instant. Heck the specific energy of any given piece of matter is c squared, but we don't (as of yet) know how to get it out except under a few very special circumstances :)