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: The magnitude of torque

  1. Oct 4, 2007 #1
    [SOLVED] the magnitude of torque

    1. The problem statement, all variables and given/known data
    Determine the magnitude of the torque about A by evaluating lABxFl (the magnitude of vector AB cross vector F) where AB = -15i + 12j and F= -200lbs (cos theta)i - 200lbs (sin theta)j

    2. Relevant equations
    cross product and maybe the magnitude of torque

    3. The attempt at a solution
    so i did the cross product and ended up with
    k = (-15(-200 sin theta))-(12(-200cos theta)) whick i simplified
    to 3000(sin theta) + 2400(cos theta)

    so k = 3000(sin theta) + 2400(cos theta)

    so am I done or should I take the sqrt of the values = to k ??
    the problem i have with this is theta is undefined and i would end up with a more complicated expression.
    so what do i do
  2. jcsd
  3. Oct 5, 2007 #2


    User Avatar
    Science Advisor

    That is not "k= ". What you have is the coefficient of k (unit z-vector). The magnitude is the value of that coefficient. If you wanted to be real technical, the "magnitude" is the square root of the square of that: its absolute value and so just what you have as long as it is positive.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook