I don\'t know how to do part (b), anyone can help? Thank you ! A truck engine tr

Question

I don't know how to do part (b), anyone can help? Thank you !

A truck engine transmits 31.0 kW (41.6 hp) to the driving wheels when the truck is traveling at a constant velocity of magnitude 75.0 km/h (46.6 mi/h) on a level road, What is the resisting force acting on the truck? 1488.0000238 N Assume that 66% of the resisting force is due to rolling friction and the remainder is due to air resistance. If the force of rolling friction is independent of speed, and the force of air resistance is proportional to the square of the speed, what power will drive the truck at 37.5 km/h? At 150.0 km/h? Give your answers in kilowatts and in horsepower. v = 37.5 km/h p = kw p = hp p = kw p = hp v= 150.0 km/h.

Explanation / Answer

velocity
V = 7500 / 3600 = 2.0833m
force    F = P / V = 31000 / 1.6666 =1488 N

b) The speed is lowered by a factor ofone-half, and the resisting force is lowered by a factor of(0.66+0.34/4) and sothe power at the lower speed is       p = 31 *(0.5)(0.66+0.34/4) =11.54 kw
                                                  =15.47 hp
    Similarly, at the higher speed,      p = 31 *(2 )(0.66+0.34/4) = 46.19 kw
                                              = 61.92 hp

b) The speed is lowered by a factor ofone-half, and the resisting force is lowered by a factor of(0.66+0.34/4) and sothe power at the lower speed is       p = 31 *(0.5)(0.66+0.34/4) =11.54 kw
                                                  =15.47 hp
    Similarly, at the higher speed,      p = 31 *(2 )(0.66+0.34/4) = 46.19 kw
                                              = 61.92 hp
    Similarly, at the higher speed,      p = 31 *(2 )(0.66+0.34/4) = 46.19 kw
                                              = 61.92 hp

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