1. The problem statement, all variables and given/known data "One gallon of gasoline contains 3.1*10^7 calories of potential energy that are released during combustion. If 1 gal of gasoline can provide the force that moves a car through a displacement of 25 mi, what is the average force produced by the gasoline?" 2. Relevant equations This is where I am confused. All of the equations I can think of for average force require velocities, mass, time, etc. and I don't see how to get from here to there. Right now I am just using 1 cal = 4.18 Joules and 1 mi = 1609.3 m. 3. The attempt at a solution Assuming complete efficiency, 3.1*10^7 cal / 25 mi = 1.24 * 10^6 cal / mi then multiply that by 4.18 Joules/1 cal and by 1 mi/1609.3 m to get 3220.8 J/m (or N). This could of course be multiplied back out to "work", but that strikes strikes me as circular. I just don't know if the answer I have is reasonable/what the question wants, since it's flagged as difficult and I haven't done anything but convert units. What am I missing?