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: Torque and vectors

  1. Jul 6, 2014 #1
    1. The problem statement, all variables and given/known data
    So I was wondering how do we account for vectors that are at a certain angle. The problem that I'm having with the picture is: if I was calculating torque from point B, how would I account for the vector G.

    2. Relevant equations

    3. The attempt at a solution
    I've tried taking the component that's vertical to the slope, but in that case what is the lever arm? Is it where the vector G crosses the slope(point D)?
  2. jcsd
  3. Jul 6, 2014 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Try taking the component that's perpendicular to the ramp (incline).

    Do you know about the line of action for a force -- in this case force G ?
  4. Jul 6, 2014 #3
    I've tried taking the perpendicular component, but not sure what the lever arm is. I'm not sure how to determine the line of action.
  5. Jul 6, 2014 #4
    By extending the force T, you can see that it will contact point D. So it is like you're applying the force T directly on point D and the lever arm will be BD. Then take the perpendicular component of force T relative to the slope.

    You can always check.
    If we assume that BT is perpendicular to force T (note: BT is the dist. bet. B and T)
    From the figure, the τ = T*(BT) . But, BT = BDsin(90-α). Therefore τ = T*(BDsin(90-α)) [1].
    Returning to your problem, τ = Txr where r is the lever arm. The perpendicular component of T is Tsin(90-α). Therefore τ = Tsin(90-α)*r = T*(BDsin(90-α)) from [1]. Therefore r = BD.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted