Hello! I\'ve got a question on how to find the answer to this problem: Problem t

Question

Hello!

I've got a question on how to find the answer to this problem:

Problem text:To estimate the effect needed to keep a certain car at a constant velocity 60 km/h, the described test was done on a horizantal road: The car was accelerated up to 65 km/h. Then the engine was decoupled. The velocity then decreased to 55 km/h after 7.2 s. The mass of the car (including driver and passenger) was 1450 kg. How large is the desired effect?

The answer shall be approximately 9,3 kW, according to the answer key of my book, but I am not quite

I don't quite understand how to calculate the effect the problem is asking for. I am not accustomed to this approach to find an effect, for that reason I have trouble with understanding what the problem is asking me for. Shall I find the average effect in the speed area 55-65 km/h, or is there a way to calculate the effect at exactly 60 km/h, when I know the given values?

Many thanks in advance !!!

Explanation / Answer

Initial energy = 1/2 mV^2 Final energy = 1/2 mu^2 V =65*5/18 m/s u =55*5/18 m/s Power =1/2 m*[V^2-u^2] /t =9.323 KW

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