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Homework Help: Surface Integral of Vector Fields

  1. Apr 26, 2009 #1
    Evaluate the surface integral ∫∫S F · dS for the given vector field F and the oriented surface S. In other words, find the flux of F across S. For closed surfaces, use the positive (outward) orientation.
    F(x, y, z) = y i + x j + z^2 k
    S is the helicoid (with upward orientation) with vector equation r(u, v) = ucos(v)i + usin(v)j + v k, 0 ≤ u ≤ 3, 0 ≤ v ≤ 3π.

    ∫∫S f*dS=∫∫D F*(r_u x r_v)dA

    i got int[0,3] and int[0,3pi] usin(v)^2-ucos(v)^2+uv^2dvdu
    i do not know how to integrate this(yeah, shame on me) and i dont know if this integral is correct
  2. jcsd
  3. Apr 26, 2009 #2


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    It looks ok to me. What's stopping you from doing it? First integrate dv and then the result du. No special tricks needed. Though you could simplify u*(sin(v)^2-cos(v)^2).
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