Surface intersected by line parallel to x-axis

Click For Summary
The discussion revolves around evaluating the integral I over a surface S intersected by a line parallel to the x-axis. Participants are tasked with showing that dS can be expressed as dS=|\nabla f|/(∂f/∂x) dy dx. The conversation highlights uncertainty about the function f and its implications for the integral. Additionally, there is a focus on how to manipulate the integral to express it in terms of the gradient of f. The thread emphasizes the importance of understanding the relationship between the surface and the function for solving the problem.
wifi
Messages
115
Reaction score
1
Problem:

Consider ## I=\int_S \vec{v} \cdot d \vec{S}=\int_S \vec{v} \cdot \hat{n} dS##, where S is a surface that is intersected once by an line parallel to the x-axis. Show that dS=\frac{|\nabla f|}{\partial f/ \partial x}dy \ dx, and that therefore, I=\int_S \vec{v} \cdot \frac{\nabla f}{\partial f/ \partial x} dy \ dz

Attempt at a Solution:

Not really sure where to start...:confused:
 
Physics news on Phys.org
hi wifi! :smile:

what do you think f is? :wink:
 
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 4 ·
Replies
4
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
3
Views
2K
Replies
6
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
Replies
2
Views
1K
  • · Replies 6 ·
Replies
6
Views
3K
Replies
6
Views
3K
Replies
5
Views
2K