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Power loss question

  1. Oct 6, 2011 #1
    You are testing a new car in a wind-tunnel for road and wind resistance. At a speed of 75.0 Km/hr you have found that 63.0 % of the total output power of an automobile engine is used in overcoming the resistance of the road and wind against the movement of the car. If the output power of a particular car engine is 69.00 HP, what is this resistance (ie. what is the force)? Give your answer in Newtons. (Take one HP as 746 Watts.

    so i was like calcualting it like this

    and 60% of 51474 is 32428.62

    then i did the formula of the power


    and got that answer but it is wrong

    can anyone explain to me what i did wrong here
  2. jcsd
  3. Oct 6, 2011 #2


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    Well, you stopped showing your calculations after figuring the power used to overcome wind resistance. I don't know what you did to calculate the force, but did you check the units of your calculations all the way thru?
  4. Oct 6, 2011 #3


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    As SteamKing mentione, you didn't mention what units you used for the terms in power = force x speed. It would help us to help you if you showed more of your work.
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