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Homework Help: Find the magnitude of the torque

  1. Feb 12, 2009 #1
    1. The problem statement, all variables and given/known data
    Find the magnitude of the torque about P if a 68 lb force is applied as shown. Give your answer correct to the nearest integer.
    12-4-40.gif


    2. Relevant equations
    t=r X F


    3. The attempt at a solution
    t = (4)(68)(sin30)
    = 136
     
  2. jcsd
  3. Feb 12, 2009 #2

    LowlyPion

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    Homework Helper

    Re: Torque

    Don't you want to consider the distance at which it is acting is 4*√2 ?

    At the point of interaction then the ⊥ component of F looks to me like F*Cos15°
     
  4. Feb 12, 2009 #3
    Re: Torque


    You wrote what must have been intended to be a vector equation for the torque, t = r x F, because the cross product only makes sense if t, r, and F are all expressed as vectors. But then you proceeded to do a scalar calculation. Why not make your torque calculation in vector form using the determinant expression for the cross product and giving the resulting torque as a vector? Then if you need the magnitude of that vector, dot it with itself and take the square root of the result.
     
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