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Homework Help: Net Work

  1. Oct 17, 2005 #1
    The drawing shows a boat being pulled by two locomotives through a canal of length 2.39 km. The tension in each cable is 4.17E4 N, and = 16.7°. What is the net work done on the boat by the two locomotives?

    first I used W=fd... i multiplied 4.17E4 * 2 = 8.34E4 to get the total tension in each string. then to get the total work i multiplied that by 2390 (m) = 1.99E8... i divided that by two to get the work in each string = 9.97E7... then i realized that would be the tension in each string if the string was perpendicular to the boat so i found the hypotenuse using cos(16.7)=9.97E7/H that gave me 1.04E8. in order to get the net work i multiplied that by two becuase there are two strings and i got 2.08E8 J. that answer is wrong and i can't figure out why... can someone help please?! thanks!
     
  2. jcsd
  3. Oct 17, 2005 #2

    hotvette

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    Your approach seems correct. You may have a math mistake somewhere. I got 1.91E8 J.
     
  4. Oct 17, 2005 #3

    Fermat

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    Looks like you divided by cos(16.7) instead of multiplying by it :smile:

    I got the same as Hotvette.
     
  5. Oct 17, 2005 #4
    but if i am trying to find the hypotenuse of the triangle... shouldn't i divide instead of multiply?
     
  6. Oct 17, 2005 #5

    hotvette

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    The tension on the cable represents the hypotenuse. What you want is the component in the direction of travel.
     
  7. Oct 17, 2005 #6
    oh thank you!!!
     
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