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Homework Help: Equilibrium at Constant Velocity

  1. Sep 26, 2004 #1
    Hey there,

    I have a problem that seems easy to me to solve but I'm just not getting it. I'll give the problem and then what I've done so far.

    A helicopter is moving horisontally to the right at a constant velocity. The weight of the helicopter is W = 51200N. The lift force L generated by the rotating blade makes an angle of 21.0 degrees with respect to the vertical.

    (a) What is the magnitude of the lift force?
    (b) Determine the magnitude of the air resistance R that opposes the motion.

    So I started out by drawing my free body diagram, making my component vector chart.

    I have 3 forces acting on the helicopter; L, W, and R

    For the L force:
    x component = Lcos21.0 degrees
    y component = Lsin21.0 degrees

    For the W force:
    x component = 0
    y component = - W

    For the R force:
    x component = - R
    y component = 0

    So when adding up my x components my equation looks like:
    Net force of x = Lcos21.0 degrees - R

    and my equation for the y component looks like:
    Net force of y = Lsin21.0 degrees - W

    But when solving for these equations I don't get the right answer. Where am I going wrong?

    Thanks for any help provided.
  2. jcsd
  3. Sep 26, 2004 #2
    For the L force:
    x component = Lcos21.0 degrees
    y component = Lsin21.0 degrees
    Answer : Suppose to be the other way round.
  4. Sep 26, 2004 #3
    Well, thank you Leong. That did it. Unbelievable that something like that was giving me grief.

    Thanks again.
  5. Sep 26, 2004 #4
    Glad i can help.
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