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Homework Help: Work done by normal foce

  1. Jan 30, 2012 #1
    I have become very confused after i tried to solve this question.
    A rope pulls a 2 kg object straight up, accelerating it from rest at 2.2 m/s^2 for 3 seconds.
    they want the work done by each force acting on it.
    Ok i found the displacement as 9.9 m up. Then i found out that the applied force does 43.56 J and that Fn does 150.678 J and gravity does 194.238 J .

    Then they ask for the total mechanical work done. I just added the works and got -.678 . Then they ask for the net force which is 4.4 N up and work done by the net force which is 43.56 J.

    I am confused about finding the net work when fg,fn, fapp are involved what am doing wrong. Also when solving other questions do i include fn and fg when the displacement is vertical?

    Please help and thank you. i would add more detail but i got no time to study.
  2. jcsd
  3. Jan 30, 2012 #2
    E initial = E final

    0 = - mg*X + F*X + mV^2/2

    You can figure out all three.

  4. Jan 30, 2012 #3
    I am sorry but i don't understand your formula. yes, i know that initial potential and kinetic energy equal the final but the next line i don't understand what it is nor how it can help.
  5. Jan 30, 2012 #4


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    Staff Emeritus
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    Homework Helper

    What is Fn, a normal force? Are you sure there is a normal force acting on the object while it is accelerating upward?
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