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Homework Help: Plumb Question.

  1. Jun 14, 2007 #1
    Please Help! Plumb Question.

    1. I can't figure this out for the life of me. "A plumb line hangs from the ceiling of a jumbo jet's passenger cabin. When the planes is at rest on the rumway, th plumb line is vertical. As the plane accelerates it is observed that the plumb line makes an angle a C with respect to the vertical. What is the plane's acceleration."

    I want to say that this involves using the equation (a of x)/(g)+(a of y)= tan (c+90) Am I correct?
  2. jcsd
  3. Jun 14, 2007 #2
    Start by drawing a free body diagram that analyzes the forces acting on the plumb bob. You know there must be a net force because there is an acceleration; just keep that in mind when drawing the diagram and you should be able to reason through the rest.

  4. Jun 16, 2007 #3
    The thing is even looking at the free body diagram I'm lost. There is no mass given for the plumb bob which throws off half of my equations. I just want to know If I'm on the right track.
  5. Jun 16, 2007 #4


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    Force equals mass times acceleration! In particular, the horizontal component of force equals the mass of the bob times the acceleration. You are correct (here is where you need the "free body diagram) that the horizontal component of force (mass times acceleration) divided by the vertical component of force (mg) is equal to the tangen of the angle- but your equation should be (ma)/(mg)= cos(C). Notice that the mass cancels out.
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