How Is Economical Speed Calculated for Fuel Efficiency?

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Economical speed is defined as the fuel-efficient speed for a car, calculated using the formula e = vt/(kv3t + Pt), where e represents fuel efficiency, v is speed, P is power, and k is a constant related to resistance. The resistance force is expressed as F = kv2, and energy for resistance and base power must be considered separately. It's noted that the engine's force must equal the resistance force for constant speed, indicating that energy should not be combined in the work calculation. Additionally, fuel efficiency is influenced by engine specifics beyond just resistance force calculations. Further considerations for calculating economical speed should include these engine details for more accurate results.
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This is my first writing in forum. And I'm not good at English... Please understand my poor writing.

Resistance force : F=kv2 (N)
Base puissance : P (W)
Time : t

Fuel-efficiency : e (m/J)
Economical Speed is fuel-efficient speed for a car. (e is maximum)

Energy for resistance force must be kv3t
Energy for base puissance mush be Pt
Fuel-efficiency e must be vt/(kv3t+Pt) = v/(P+kv3)

Is there something I have to consider more??
Or please suggest some other method to get economical speed.
 
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I don't think you can get fuel efficiency from this setting of the problem.
The force from the engine (the one associated with power) should be equal to the resistance force, for motion with constant speed. You don't use energy for both of them so there is no reason to add them in calculating the work done.

Fuel efficiency depends on the details of engine, not just on the expression for resistance force.
 
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