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

Magnitude and angles of a force

  1. Aug 31, 2011 #1
    1. The problem statement, all variables and given/known data
    a force is given by F= 20i - 60j + 90k N. Find its magnitude and the angles it forms with the coordinate axis.

    2. Relevant equations
    F = magnitude of F times the unit vector
    magnitude is square root (Fx squared + Fy squared + Fz squared)
    and the unit vector can be written as (cos(theta)x)i + (cos(theta)y)j + (cos(theta)z)k
    x for x component
    y for y component
    z for z component

    to find the angle of the x component: inverse cosine of Fx/magnitude

    3. The attempt at a solution
    For the magnitude I got 110
    for the angles with respect to x, y, z: 79.5, 123.1, 35.1

    please tell me if i did something wrong! thanks
  2. jcsd
  3. Aug 31, 2011 #2


    User Avatar
    Homework Helper

    That should be correct.
  4. Sep 1, 2011 #3


    User Avatar
    Homework Helper

    Agree. All looks good.
  5. Sep 2, 2011 #4
    If a textbook or something gives a different answer, it's possible the angle is in another measurement, for example radians.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook