1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    69HP=51474
    and 60% of 51474 is 32428.62

    then i did the formula of the power

    power=forcexdistance/time

    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

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    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

    rcgldr

    User Avatar
    Homework Helper

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook