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: Statics Problem - understanding the directions.

  1. Dec 13, 2009 #1
    1. The problem statement, all variables and given/known data
    Ok so basiclly I know how to do the problems, but i'm confused when to make the force negative and when to ignore the negative.

    forexample: http://yfrog.com/jastaticsprobp
    solving part a:
    Moment at A = -24*39 -(-14*39) = 2028
    notice how i had to do -(-14*39) to compensate for the force going down



    where solving for
    Moment at xaxis= -230*.250- 230*.210 = -105.8
    notice i did not do -(-230*.210)

    My assumption?
    either keep the direction of force if the problem is 2-D ?? i have no idea, can someone help make this clear? thanks
  2. jcsd
  3. Dec 13, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi kpx001! :smile:

    "up" and "down" doesn't matter, what matters is "clockwise" and "anti-clockwise" …

    so in both your pictures, the torque (the moment) is clockwise for both forces, so they have the same sign (and your answer to the first is wrong). :wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook