Finding force and friction coefficient from fuel energy in a car

[pippintook]

A gallon of gasoline has a chemical PE of 1.2 x 10^8 J. If a 2000 kg car gets 40 km/gallon, what is the average force on the car? Assume constant speed and remember the force on the car is applied over the total distance traveled. What is the coefficient of friction?

I tried PE = mgx, using m = 2000 and solving for x (which was 6122.45). I'm not really sure where to go from there though.

 

[LowlyPion]

Not quite.

The PE of the gasoline is not gravitational PE. Completely different.

This PE gets converted into work over the distance of 40 km.

What you do is convert the energy they gave you into the work to move the car. Work is F*d.

At constant speed then the force retarding motion is consumed by the combustion of the gas.