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Homework Help: Work and energy difficulty

  1. Apr 17, 2008 #1

    ka7

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    [SOLVED] Work and energy

    Hello, I've been having difficulty with this question...
    1. The problem statement, all variables and given/known data

    A 25.6kg child pulls a 4.81kg toboggan up a hill inclined at 25.7° to the horizontal. The vertical height of the hill is 27.3 m. Friction is negligible. Determine how much work the child must do on the toboggan to pull it at a constant velocity up the hill.



    2. Relevant equations

    W=FD COS (ANGLE)

    3. The attempt at a solution

    I tried using the equation above...and i tried adding the masses ...I got the wrong answer. The force, I used F=mg
    w=mgd cos (angle)
    =(4.81) (9.8) (27.3) cos (25.7)
    =1.15 x 10^3 J
    the answer 1.29 x 10^3 J but i'm not geting that...:confused:
     
  2. jcsd
  3. Apr 17, 2008 #2

    Hootenanny

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    Staff Emeritus
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    Welcome to the forums ka7,

    HINT: What is the change in gravitational potential energy of the toboggan? (Much easier :wink:)
     
  4. Apr 17, 2008 #3
    You should recheck what the D in your formula means. It is presumably NOT the vertical height of the hill.
     
  5. Apr 17, 2008 #4

    ka7

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    Thanks, i figured out what i was doing wrong:smile:
     
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