The US uses about 8 x 1019 J of energy per year How much mas

The US uses about 8 x 10^19 J of energy per year. How much mass would that require if we could totally convert mass to energy? If the mass came from, say, turning used cars entirely into energy, estimate how many would be required?

Solution

E= mC^2

m = 8x10^19/(9x10^16) = 888.89 kg

a midsize car weight about 3000 lbs = 1361 kg

m/1361 /1361 = 0.65

only need 0.65 cars.