1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Energy audit of elec/mech?

  1. Mar 13, 2013 #1
    1. im having trouble selecting the proper equations for each stage

    2.Im not looking for anyone to do it for me , but i would appreciate if some one could tell me what EQUATIONS TO USE at each part of the question

    3. i have gotas far as question five

    Attached Files:

    Last edited: Mar 13, 2013
  2. jcsd
  3. Mar 13, 2013 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF.

    Can you show the equations and your solutions for the parts that you have done so far?
  4. Mar 13, 2013 #3
    Equations used so far

    Q1: I USED EQUATION P/real=V*I*Cos ∅
    P/real=340*4.24*Cos 45
    P/real=1019.37 (W)

    Q2:I USED EQUATION PE=MGH (mass of water =1000)
    PE= 1500*9.81*10 (gravitity =9.81)
    PE= 147150 (Joules)

    Q3:I USED EQUATION Mass Flow= Mass/time
    = 1500/480 ( 8mins =480 seconds)
    = 3.125Kg/s

    =4.24*340 OR should i of used Pout=Work done /time
    = 1441.6 =147150/480

    ??Q5 I WILL USE EQUATION Power out/Power in *100 to establish my efficency

    Im not 100% that ive used the correct EQUATIONS , as each question draws on your previous answer , Any help would be appreciated. Thanks.
    Last edited by a moderator: Mar 13, 2013
  5. Mar 13, 2013 #4


    User Avatar

    Staff: Mentor

    For Q1 I think you'll want to use RMS values of voltage and current if you're looking for power. The supplied diagram gives them as Peak values.

    Q2 is a bit vague, asking for "The energy of liquid". presumably they mean the gain in gravitational potential energy as you've done it.

    For Q4, I guess they're looking for the rate of mechanical work being done, since lifting the water is the 'output' of the system.

    For the rest of the questions, I'm afraid that I'm not very familiar with the jargon or conventions involved in fluid/electromechanical system audits...:redface: So, for example, I'm not sure what would be included in the 'specific energy' of the water leaving the pump; Does it include per unit volume kinetic energy and pressure? Gravitational potential energy too?
  6. Mar 15, 2013 #5
    Yeah, it is rather vague, but I'll motor on with what I've got... The questions seem to reflect on the answers to the previous ones... Thanks anyway D :approve:
    Last edited by a moderator: Mar 15, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted