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Question
Math
Posted 7 months ago

Suppose we have a scalar field f(x,y)=yf(x, y)=-y and a curve CC that is parameterized by α(t)=(cos(t),sin(t)1)\alpha(t)=(\cos (t), \sin (t)-1) for 0<t<2π0<t<2 \pi.

What is the line integral of ff along CC ?
Cfds=
\int_{C} f d s=

\square
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Answer from Sia
Posted 7 months ago
Solution by Steps
step 1
To find the line integral of the scalar field f(x,y)=yf(x, y) = -y along the curve CC parameterized by α(t)=(cos(t),sin(t)1)\alpha(t) = (\cos(t), \sin(t) - 1), we first need to compute the differential arc length dsds
step 2
The differential arc length is given by ds=(dxdt)2+(dydt)2dtds = \sqrt{\left(\frac{dx}{dt}\right)^2 + \left(\frac{dy}{dt}\right)^2} dt. We calculate dxdt\frac{dx}{dt} and dydt\frac{dy}{dt} from the parameterization
step 3
For α(t)=(cos(t),sin(t)1)\alpha(t) = (\cos(t), \sin(t) - 1), we have dxdt=sin(t)\frac{dx}{dt} = -\sin(t) and dydt=cos(t)\frac{dy}{dt} = \cos(t)
step 4
Substituting these into the expression for dsds, we get ds=(sin(t))2+(cos(t))2dt=1dt=dtds = \sqrt{(-\sin(t))^2 + (\cos(t))^2} dt = \sqrt{1} dt = dt
step 5
The line integral is then Cfds=02π(sin(t)1)dt\int_{C} f ds = \int_{0}^{2\pi} -(\sin(t) - 1) dt since f(x,y)=yf(x, y) = -y and y=sin(t)1y = \sin(t) - 1
step 6
Evaluating the integral, we get 02π(sin(t)1)dt=[cos(t)t]02π\int_{0}^{2\pi} -(\sin(t) - 1) dt = [-\cos(t) - t]_{0}^{2\pi}
step 7
Plugging in the limits of integration, we find [cos(2π)2π][cos(0)0]=[12π][10]=2π2[-\cos(2\pi) - 2\pi] - [-\cos(0) - 0] = [-1 - 2\pi] - [1 - 0] = -2\pi - 2
[1] Answer
2π2-2\pi - 2
Key Concept
Line Integral of a Scalar Field
Explanation
The line integral of a scalar field along a curve is found by integrating the scalar field function multiplied by the differential arc length over the parameter interval of the curve.

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