Question

A ton of coal holds about 3.2E10 J of energy and costs about 40 dollars. How many mega joules of energy in the form of coal can you get for a dollar?

Answer 1

First you must calculate the amount of energy given by one dollar of coal:

$1\ \cdot \frac{3.2\cdot 10^{10}\ J}{40\ } = 8\cdot 10^8\ J$

In order to express the result in MJ (megajoules), I'm going to use a conversion factor:

$8\cdot 10^8\ J\cdot \frac{1\ MJ}{10^6\ J} = \bf 8\cdot 10^2\ MJ$