Greens theorem-help setting up correct integral

  • Thread starter Thread starter hils0005
  • Start date Start date
  • Tags Tags
    Integral
Click For Summary
The discussion centers on applying Green's Theorem to evaluate a line integral over a closed triangular curve defined by vertices P1(0,5), P2(0,2), and P3(3,5). The vector field is given as F(x,y) = xy^2 i + 4xy j, leading to the calculation of the double integral of the difference of the partial derivatives, specifically ∫∫(4y - 2xy) dA. Participants express confusion regarding the correct limits of integration, particularly in the context of counterclockwise orientation, with suggestions that the limits should reflect the direction of traversal. There is a question raised about the validity of integrating with limits where the lower bound exceeds the upper bound, indicating a need for clarification on setting up the integral properly. The discussion emphasizes the importance of correctly determining the limits based on the orientation of the curve.
hils0005
Messages
61
Reaction score
0

Homework Statement


Use Green Theorem to calculate \oint\widehat{}F \bullet d\widehat{}r where C is the closed triangular curve oriented counterclockwise with verticies P1(0,5), P2(0,2) and P3(3,5). vectorF(x,y)= xy^2 i + 4xy j


Homework Equations





The Attempt at a Solution


I first took the partial of F2 with respect to x = 4y
partial of F1 with respect to y = 2xy

\int\int4y-2xy dA

I am not sure of what limits to use:
because it is oriented counter clockwise:
y-2\leq x \leq 0
5 \leq y \leq 2
 
Physics news on Phys.org
It looks fine except I would check your order of limits--it should be entering at x=0 and leaving at x=y-2 and it's backwards for y too--maybe that was just a mistake when you wrote it.
 
that is how I did the problem initially however, the problem says it is in the counterclockwise direction which I would think y goes from 5 to 2, and x from 0 to y-2.
(which is only half of what I did)

Can anyone explain this?
 
When you integrate a region, you do so on an interval x\in [a,b],y\in [c,d]. Does the integral make sense if a>b, c>d?
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

Similar threads

  • · Replies 8 ·
Replies
8
Views
2K
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
12
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
1
Views
2K
  • · Replies 21 ·
Replies
21
Views
4K
Replies
6
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K