(a) If the mass of 1.0 kg of coal (or any substance) could be completely converted into energy, how many kilo-watt-hours of energy would be produced?
(b) Assume that the average U. S. family of four uses 600 kWh of electric energy each month and that modern power plants are efficient in converting this released energy into electric energy. How long would this mass be able to supply the U. S. public with electric energy?