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!

Need help solving 3D

  1. Sep 21, 2015 #1
    It statics, I am having difficulty on getting perfect to read the dimensions correctly in order to find the forces!

    This photo for example


    I put B = (-3i,-2j, -6k) but correct answer is (3i,-2j,-6k) ... why 3i but not 3i ?! I'm reeally confused

    For C I put -1i but correct answer is 3i !.. how?!???

    for D I added the 1 and 2 and i put -3i , and I put -3j but correct is 3j ....

    can anyone explain and give me easier way to approach the answer and avoid mistakes?! I have an exam on friday and this is basic thing that i cant seem to understand!
  2. jcsd
  3. Sep 21, 2015 #2


    User Avatar
    Homework Helper

    For B, your positive x is coming toward you. Use the right-hand rule to keep your positive directions straight.
    C looks like it is at -3i -1j .
    D looks like it is at -2i and 3j.
    Your i components need to find references on the x axis. Your j components need references on the y axis.
  4. Sep 21, 2015 #3
    I dont get it
  5. Sep 21, 2015 #4


    User Avatar
    Homework Helper

    Look at C. The left-right line above it says that it is 1ft left of the x-axis. That means the y-component is -1.
    The long line going through C crosses the segments marked 1ft and 2ft by D. This means that C is 3ft behind the y-axis, or the x component is -3.
    Does that help?
  6. Sep 24, 2015 #5
    I understand now after doing 99999 researches and watching 9999 videos... and easier and simple is to take AB for example, find points A and B, then subtract A-B and BINGO!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Need help solving 3D