1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Having issues with units

  1. Oct 27, 2012 #1

    ISX

    User Avatar

    1. The problem statement, all variables and given/known data
    Venturi effect nozzle.. Starts off at 100cm and goes down to 40cm. The flow rate of the gas is 2.23 m3/s. What is the average velocity at the beginning and end of the nozzle.


    2. Relevant equations
    Continuity Formula, Bernelli = Q = A1V1=A2V2


    3. The attempt at a solution
    It's not the solution I am having trouble with so much, I am having a brain fart with units. I can take the area of 100cm and get 7850 cm2 and 40cm works out to 1256cm2 and you end up with a starting velocity of 0.000284 and an ending velocity of 0.001775 which I am assuming is cm/s.. Is that right or do I need to convert 100cm and 40cm to meters first and then do the calculation and then end up with meters/s?
     
  2. jcsd
  3. Oct 27, 2012 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Hi ISX. No need to assume anything here. If you carry your units along in the calculation it will guide you. You have V = Q/A. You plugged in numbers as V = (2.23 m3/s)/(7850 cm2). So, what do the units reduce to here?
     
  4. Oct 27, 2012 #3

    ISX

    User Avatar

    I guess I've never read it like you put it, just always had a guide to follow in the book. I see cubic meters and cm squared so I woulda thought you would make them both cm or both meters..so I'm still not sure.
     
  5. Oct 27, 2012 #4

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Right. You can go either way: convert the cm2 to m2 or convert the m3 to cm3.
     
  6. Oct 27, 2012 #5

    ISX

    User Avatar

    Alright so both of these should be right then.

    2cx650.jpg
     
  7. Oct 27, 2012 #6

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Yes. Nice. :smile:
     
  8. Oct 27, 2012 #7

    ISX

    User Avatar

    Schweeeeet. Thanks.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook