Line Integrals & Green's Theorem ("Take-Home" Problem)
13. (a) (4 pts) Set up and evaluate the line integral ∮_C F · dr, where C is the circle x^2 + y^2 = 9 (oriented counterclockwise) and F(x,y) = y î + 2x ĵ.
Evaluate this line integral directly — that is, find a vector function r(t) to parameterize the circle, compute dr and F(r(t)), and find limits of integration — do not use Green's Theorem. You may use a calculator or app to evaluate your integral once it is set up.
(b) (4 pts) Suppose C is any closed curve C in the xy-plane (oriented counterclockwise), and D is the region in the xy-plane enclosed by C. For which of the following vector fields F(x,y) will the line integral ∮_C F · dr equal the area of the region D? (Hint: Use Green's theorem.) Circle all correct answers.
i. F(x,y) = y î + 2x ĵ
ii. F(x,y) = -y/2 î + x/2 ĵ
iii. F(x,y) = x î + y ĵ
iv. F(x,y) = 0 î + x ĵ
v. None of the above.
(c) (2 pts) Is it possible to find a conservative vector field so that ∮_C F · dr = the area of the region D enclosed by the closed curve C? Either give an example of a conservative field that works, or explain why it is not possible to find such a field.