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202_Physics ProblemsTechnical Physics

# 202_Physics ProblemsTechnical Physics - 204 Energy and...

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204 Energy and Energy Transfer Section 7.9 Energy and the Automobile P7.44 At a speed of 26.8 m/s (60.0 mph), the car described in Table 7.2 delivers a power of P 1 18 3 = . kW to the wheels. If an additional load of 350 kg is added to the car, a larger output power of P P 2 1 = + (power input to move 350 kg at speed v ) will be required. The additional power output needed to move 350 kg at speed v is: P out = = f v mg v r b g b g µ . Assuming a coefficient of rolling friction of µ r = 0 016 0 . , the power output now needed from the engine is P P 2 1 0 016 0 350 9 80 26 8 18 3 1 47 = + = + . . . . . b gb g e j b g kg m s m s kW kW 2 . With the assumption of constant efficiency of the engine, the input power must increase by the same factor as the output power. Thus, the fuel economy must decrease by this factor: fuel economy fuel economy km L b g b g b g 2 1 2 1 18 3 18 3 1 47 6 40 = F H G I K
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