# Homework Help: Force on an orifice plate

1. Mar 19, 2015

### Jsp83

<<Moderator note: Missing template due to move from technical forum.>>

I am having difficultly with a problem in my fluid mechanics course and I'm hoping someone could help me out.

Here is a screenshot of the question I'm stuck on:

So far I have been using Bernoulli equation to find the pressure in the pipe, assuming atmospheric pressure at the point where the stream is released. This gives p1 + 0.5ρv12 = patmos + 0.5ρv22
Where v2 = v1A1/A2

I have then been using the Reynolds transport theorem to find the force on the plate:
m(v2-v1) + p1A1 = PatmosA2 + Fx
Where m is the mass flow rate, m = ρAv1
and Fx is the force I am solving for.

Can anyone find anything wrong with this method, as I have checked my calculations many times but constantly get the wrong answer.

Last edited by a moderator: Mar 19, 2015
2. Mar 19, 2015

### Staff: Mentor

The signs on some of the terms in the momentum balance are incorrect.

m(v2-v1)= (sum of forces in +x direction) - (sum of forces in -x direction)

Chet

3. Mar 19, 2015

### Jsp83

Ah, so obvious now... thanks for your help