The vehicle with mass m runs on the straight road with constant power P, and the constant speed of the vehicle is v. when the speed of the vehicle is V2, the acceleration of the vehicle is large P/mv1 B,P/mv2 C,P(v1-v2)/mv1v2 D,pv1v2/m(v1v2) What to choose Why?

You should choose C,
When the vehicle is running at a constant speed, the traction is equal to the resistance = P / V1 (P = f traction * V),
When the car is running at V2, the traction is p / v2,
So the resultant force is p / v2-p / V1, and because f is equal to Ma,
So a = P (V1-V2) / mv1v2, choose C

A car with mass m runs on a straight road with constant power P. when it runs at a constant speed, the speed is V1,
A car with mass m runs on a straight road with constant power P. when it runs at a constant speed, its speed is V1. When its speed is V2 (V2 < V1), what is its acceleration? Let the resistance remain unchanged

When the drag is equal to the traction force at a constant speed, the value is p / v1. When V2 moves, the traction force is p / V2, and the acceleration is (P / V2 - P / V1) / m

When the mass is m and the rated power of the engine is p, the vehicle runs along a straight road, when its acceleration is a,
At this time, the actual power of the engine measured is P1, assuming that the resistance in motion is constant,

Let f be the resistance in motion and Vmax be the maximum velocity
（a*m+f）*v=P1
Find the resistance F
The maximum speed is: Vmax = P △ F

The problem of automobile engine power
For example, why some cars can reach the maximum power of 70 at 5000 rpm, while some cars can reach the maximum power of 70 at 6500 rpm. I don't discuss the problem of torque. I understand this very well. The lower the speed, the higher the power. Or the higher the speed, the higher the power

Let me give you the most popular explanation: power = force × (distance / unit time)
Force - depends on displacement, fuel, ignition technology, etc
Distance / unit time - engine speed
Therefore, the power of large displacement engine at the same speed is certainly higher than that of small displacement engine. Conversely, the speed of large displacement engine at the same power is definitely lower than that of small displacement engine
Therefore, if you want the car to climb the slope strongly, accelerate fast and pull high speed, you should choose the one with low speed and high power; otherwise, if you want to save fuel and economy, you should choose the one with higher speed

The engine power of the car is 90kw, and it moves forward at a constant speed of 20m per second. (1) calculate the traction. (2) how much work does the car do per hour?

P＝Fv
So f = P / v = 900009 / 20 = 4500n
W=Pt=90*1=90kw.h=324 000 000j

The vehicle with mass m runs on the straight road with constant power P, and the constant speed of the vehicle is v. when the speed of the vehicle is V2, the acceleration of the vehicle is large P/mv1 B,P/mv2 C,P(v1-v2)/mv1v2 D,pv1v2/m(v1v2) What to choose Why?