The vector field has components . Consider the integration path , which is a semicircle starting at and ending at (see "details" section). The diameter of the semicircle is , and its radius is .
What is the maximum possible value of the line integral of the vector field over the path, given the constraints on the path?
Details and Assumptions:
1)
Vector
is a unit-vector in the direction of
2)
Vector
is a unit-vector perpendicular to
, which remains constant over the path
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p1 = { 0 , 0 , 0 }
p2 = { 1 , 2 , 3 }
center = 2 p1 + p2 = { 2 1 , 1 , 2 3 }
radius = EuclideanDistance [ p1 , center ] = 2 7
The unit vectors that used: ⎝ ⎜ ⎜ ⎛ − 1 4 1 1 4 1 3 0 − 7 2 − 9 1 2 − 1 3 3 − 1 4 3 − 1 8 2 3 1 3 2 ⎠ ⎟ ⎟ ⎞
Scale a vector v back to original coordinates: radius v + center ]
Compute a coordinate from \tau), the path integration variable, and θ , the angle the path is displaced. { 2 1 ( 1 3 cos ( θ ) cos ( τ ) + sin ( τ ) ) , − 1 3 cos ( θ ) cos ( τ ) − 3 2 6 7 sin ( θ ) cos ( τ ) + sin ( τ ) , 2 1 3 cos ( τ ) ( 2 1 4 sin ( θ ) − 3 cos ( θ ) ) + 2 3 sin ( τ ) }
The integral: ∫ 0 π 5 4 0 8 5 2 1 4 sin ( 2 θ ) ( 4 9 sin ( τ ) + 6 1 sin ( 2 τ ) ) sin 2 ( 2 τ ) − 1 0 4 sin 3 ( 2 τ ) cos ( 2 τ ) ( cos ( 2 θ ) ( cos ( τ ) − 3 7 ) + 4 0 3 cos ( τ ) − 2 9 9 ) + 1 3 1 3 cos ( θ ) sin 2 ( 2 τ ) ( 3 8 cos ( τ ) − 4 5 3 cos ( 2 τ ) + 4 1 1 ) + 1 3 1 8 2 sin ( θ ) sin 2 ( 2 τ ) ( − 8 6 cos ( τ ) + 8 1 cos ( 2 τ ) + 2 5 ) − 1 3 sin 2 ( τ ) cos ( τ ) ( 9 4 3 1 4 sin ( 3 θ ) + 9 1 9 cos ( 3 θ ) ) d τ = 6 2 4 1 ( 5 0 1 4 sin ( 2 θ ) + 5 1 π 1 8 2 sin ( θ ) + 2 2 4 cos ( 2 θ ) + 2 9 4 π 1 3 cos ( θ ) + 2 6 0 0 )
Maximize the result over θ and evaluate the maximization result numerically. The maximum is 1 0 . 9 5 9 6 1 7 7 7 7 4 . The angle from u 2 is 0 . 5 2 4 7 6 9 6 2 3 1 4 9 radians.