What is the friction when the car accelerates at a constant speed? Is it resistance? Is the car propelled by the ejector or towed by the trailer in front? In these two cases, the tires of the car actively rub the ground, producing rolling friction and pushing the car forward. This kind of friction is power! In other words, the friction of the ground is its traction! What about resistance? Of course there is. Air produces resistance to moving objects, and the resistance increases with the increase of speed. This is the real resistance when the car accelerates at a constant speed. In actual operation, to maintain a certain speed, the driver needs to step on the accelerator lightly and continue to refuel the engine a little. This is to overcome air resistance.
Ok, let's expand it. What about when we slow down? This situation is very complicated. In the first case, leg cramps, let go of the accelerator and see if you are a manual or automatic car. If it is an automatic car, it must be because the air resistance can't be overcome, and the tires have to drive the clutch, reducer and engine to rotate (this kind of car can't be underestimated, especially in the United States, the transmission is quite tight, and some cars don't need manual braking when parked on the slope). The rolling friction of the tires consumes some kinetic energy, so the speed will drop faster. If it's a manual car, it depends on whether you step on the clutch or not! If you don't step on anything, it has the same effect as automatic gear; But if my other foot has nothing to do with the clutch, then the tire doesn't need to drive that pile of things. This is called a "floating car". You can fly for a long time just by overcoming air resistance and tire rolling friction. Finally, there are two other situations when you step on the brakes, or when you don't practice drifting well and need the handbrake to help you play. If you buy a domestic broken four-wheel, without ABS, the tire will be locked in the end. The best calculation at this time is the simplest sliding friction. This car has ABS anti-lock, and your car will experience rolling friction and sliding friction, and finally stop with sliding friction.
I will answer your questions one by one and see that none of them come to the end. Criticize you first!
"I think V is determined by A" is wrong. Speed is determined by initial speed, acceleration and time, which cannot be taken for granted.
"And A is determined by the resultant force F." In the case of constant mass, the acceleration is indeed determined by the resultant force, but I don't find anything wrong with this formula. The reason is that you don't know the origin of V in this formula at all.
Let me deduce this formula for you:
W=P*t
P=W/t W=F*S
P=F*S/t (this step is the key) = f * v.
The speed in the formula is not the speed at a certain moment (that is, the speed calculated by the acceleration you understand), but the average speed of S's displacement in t time (S/t in the formula, you should be able to read the meaning of the formula, and the explanation of the basic formula is not given for nothing). If the initial speed of this car is not 0 and the running time is not told to you, can you calculate its average speed through acceleration? Now we understand the source of speed, but what about this force F? What is force? Then we should start from the source. Source is the backbone of the problem. Too bad you didn't give it. The question will clearly tell you what kind of power did it! And I have a feeling that power must be the main force to do work. So the formula must be: traction power = traction * average speed.
If you simply regard traction power as engine power, then this baby will be completely destroyed. The engine converts heat energy into kinetic energy, but the power varies with the amount of oil. The maximum output power of this engine may be produced under the condition of sufficient fuel supply, sufficient oxygen and sufficient combustion, but the power will inevitably change with a small step on the accelerator. The power required to overcome air resistance is naturally different with different speeds. At the same time, because the reducer, clutch and tire rolling friction are all related to efficiency, that is to say, according to the calculation results of traction force, they must be connected through a series of calculations and processing such as coefficient, inertia moment and torque. So this formula is not aimed at engine power, but only at traction power.
It is estimated that the practical application of this formula can only be used in automatic transmission cars. By avoiding manual gear shifting, the engine output power can be set at a relatively large value at one time. The advantages are that good acceleration is achieved, and energy loss caused by unstable engine power output and frequent gear shifting is avoided, saving worry and fuel. It seems that this country is far-sighted, knowing that China runs everywhere and Li Xia will run an automatic family car sooner or later.