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W=Fd, Work & Newton's Second Law problem

  1. Oct 10, 2009 #1
    [SOLVED] W=Fd, Work & Newton's Second Law problem

    1. The problem statement, all variables and given/known data

    a) Find the force to give a helicopter of mass M an acceleration of 0.10g upward
    b) Find the work done by this force as the helicopter moves a distance of h upward.

    2. Relevant equations


    3. The attempt at a solution

    Personal Note: Q10 p. 145 Challenger.

    This question isn't in the answer key, this post is mostly to verify my answer and figure it out if it's wrong.

    I first stated F = Ma, then stated a = 0.10 x 9.8 m/s^2 = 0.98 m/2^2

    Then for my answer, i had [tex]F=M(0.98_{m/s^2})[/tex]

    would that be the proper way to state that answer?

    I stated W = Fd
    Then stated W = M(0.98m/s^2)h

    is this correct?

    Last edited: Oct 10, 2009
  2. jcsd
  3. Oct 10, 2009 #2


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    Homework Helper
    Gold Member

    For part a), the net force=0.1g


    [tex]0.1g=F_{net}=\sum F[/tex]

    You should be able to find the correct, applied force on the helicopter.

    Part b) is done correctly, except you need to use the correct [itex]F_{applied}[/itex]
  4. Oct 10, 2009 #3
    Oh, this isn't the first time questions worded with g and a coefficient has stumped me.

    g = 9.8 m/s^2 right?

    oh.. so your saying an acceleration of 0.1g so F = 0.1(9.8)?

    I have trouble understanding exactly how it's asking for what... it's asking.
  5. Oct 10, 2009 #4
    You aren't asked about the net force. You are asked what force it would take to raise the helicopter with a constant acceleration of [tex]0.1 g[/tex]

    What forces act on the helicopter? There's [tex]F_{applied}[/tex] as GO1 mentioned, but there is another force acting on the helicopter as well.

    Find out what force that is, plug everything into Newton's Second Law and isolate for [tex]F_{applied}[/tex] from there on out, you're good to go. :)
  6. Oct 10, 2009 #5
    So: Fapplied = M(0.1g) + mg?
  7. Oct 10, 2009 #6


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    Homework Helper
    Gold Member

    Correct!, except the "m" in the second term, should be "M" in the notation of the problem. There is only one mass, M.
  8. Oct 10, 2009 #7
    Thanks for all your help guys!
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