Let’s say we are driving from A to B. The beginning of the drive starts with a steep uphill, but the remaining drive is long and downhill. Points A and B are the same elevation. Which direction (A to B or B to A) is more energy efficient (less fuel consumption)? Or is it maybe equal?

Question

EDIT: I am discussing real world scenario in a car. I will definitely check the fuel consumption next time I drive from Reykjavík (B) to Hveragerði (A) (and back) here in Iceland. Thanks for great answers 🙂

In: 1

Answer 1

Steep uphill first is your most efficient if the downhill is enough to overcome friction. With engine running, the shorter distance of higher load means less total power loss (the engine is moving with a certain efficiency this is separate from the car moving) so basically you get to the top and cut off the engine, gravity does the rest, the forces of friction mean less braking (loss of work energy to heat) which is energy from the engine.