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7r physics #63

Discussion in 'MCAT Study Question Q&A' started by MikeMitchell, Aug 10, 2011.

  1. MikeMitchell

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    [​IMG]

    We can rule out A and C and I understand both. The obvious answer to me thats left is choice B, which is incorrect. I don't understand how you can clearly state that rolling resistance is reduced and fuel efficiency is unaffected. I know this to be true. The answer key states that the efficiency of the engine is independent of the tires. There are obviously more factors that affect fuel efficiency other than the engine, such as aerodynamics.

    I see that higher air pressure might not be required due to the new circumstances from the passage, but this doesn't seem as good of an answer as B. Harder rubber will intuitively required more air pressure due to is resistance to deform.

    Show me the light.

    Thanks.
     
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  3. Bumbl3b33

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    Why would engine efficiency change? The engine will still burn the same amount of energy to create torque on the wheels, regardless of what the tire is made of or how much friction the car is encountering. Efficiency is just energy output/energy input times 100
     
  4. mikexima

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    this question is bogus. fuel efficiency of the engine is DIRECTLY affected by hundreds of external factors. heavier tires, larger rims, weight of passengers, going uphill, aerodynamics and what not all affect fuel effciency.
     

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