# Homework Help: Force on a plate from a fluid line source

1. Dec 9, 2015

### Raptor112

1. The problem statement, all variables and given/known data
A line source of strength 2$\pi$m is located $a$ distance a above a horizontal plate. Find the force per unit width on the plate, ignoring gravity and taking the pressure below the plate to be uniform and equal to the stagnation pressure of the fluid. (You may nd the substitution $x = a tan(\theta)$ useful in evaluating any integral that arises.)

2. The attempt at a solution
$F = - \int p \hat{n} dl = - \int_{-\infty}^{\infty} p \hat{n} dx, \hat{n} = \hat{j}$ $p$- pressure

2. Dec 9, 2015

### Staff: Mentor

Are you familiar with the method of images?

3. Dec 9, 2015

### Raptor112

Place a source of equal strength at a distance $a$ below the horizontal plate so the total complex potential becomes

$w(z) = mlog(z^2+a^2)$

but how will that give me the pressure at the boundary?

Last edited: Dec 9, 2015
4. Dec 9, 2015

### Staff: Mentor

If you have a single line source, then it is easy to get the velocity at a radial distance r from the source. You can then use Bernoulli's equation to get the pressure at that location, assuming that the pressure and velocity at infinity are zero.