Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Understanding how to solve this set

  1. Feb 12, 2012 #1
    1. The problem statement, all variables and given/known data
    Hello guys, I have a physic class this session and I'm self-teaching myself most of the material. It's going not too bad so far but I have come across a form of solving I have not seen before and would like to understand how it works. I have the data and the answer, I just don't know how to get the answer from the equation. This is the last part of a problem I have to solve that deal with the moment of a force about an edge.

    2. Relevant equations
    For easier format, here is a picture:
    http://unwantedcreations.com/img/physic_1.png [Broken]
    First line is λ of the edge
    Second line are the coordinate of the point of application of force F
    third line are the components x, y and z of the force F.

    in case you don't get it at all, here is the problem and solution:

    3. The attempt at a solution

    Ok so I think I get where -25.363 come from, if you take 0.99228 * -1.8 * 14.2 it does make -25.363, but where does -10.5678 comes from? No idea.

    Thank you for your time guys.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Feb 12, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    hi ucflap! :smile:
    it's 0.124035*6*14.2 …

    to calculate a determinant, you multiply one element from each row and column, ie you zig-zag in every possible way

    there are only two zig-zags that don't include a 0, and 0.124035*6*14.2 is one of them :wink:

    (to see why it's minus, look up a book or wikipedia on determinants)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook