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Zamorush,
I am convinced this is Newton's Second Law. I'm afraid I don't really understand your working.
The Force I am referring to is the force produced by the engine to accelerate the car. It's 230bhp multiplied by a constant which determines how much of that bhp actually gets transmitted to the road multiplied by some constant to convert that to Newtons. Gravity neither helps nor hinders the acceleration on a flat road (and in any case is constant).
v-u is constant. Acceleration is final speed (v) - initial speed (u) over time (t). Since we are talking 0-60 time, (v-u) is (60 - 0) * a constant to convert that to m/s.
If you think about it, it can only be N2L. We are calculating the acceleration of a mass, the only tricky bit is finding the right constant (fudge factor) to convert the bhp produced by the engine to the resultant force in newtons that is actually being applied to accelerate the mass.
This constant would have many components, including the frictional forces you mention. But it would be too complex to calculate it. I'll bet they came up with the 0.9 by feeding in the figures from hundreds of different cars and taking an average.
Have I convinced you?
Phil.
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