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Re: [Phys-l] horsepower

On 11/15/2007 02:35 PM, Anthony Lapinski wrote:
For an "average-size" car, is there a general rule of thumb or formula
that relates horsepower and speed?

No. There's a lot more to it than "size". Some shapes
are vastly more aerodynamics than others.

I read that it takes 20 hp to drive at
60 mph. Another source said 40 hp is needed to go 80 mph. I realize air
resistance increases with the square of the speed, so those numbers seem
to make sense.

No, they don't make sense. The parasite drag force goes like
airspeed squared, but the power required goes like the *cube*.