Question

Burning coal yields about 30 ⋅ 106 J of energy per kilogram of coal burned. Assuming that the coal power plant is 30% efficient, how much coal has to be burned to light the bulb for a day?

Answer 1

That light bulb was 8.46E6 joules per day

Answer 2

Assuming the bulb is on for 24 hours, it have a power of roughly 98W, so that's a reasonable light bulb power. As for the question, efficiency is defined as follows:\[\eta =\frac{ E _{Out} }{ E _{In} }\]You should be able to use that equation to help you.