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Calculate the z component of the torque relative to position

  1. Mar 31, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img3.imageshack.us/img3/5681/32832.jpg [Broken]

    All seven forces have a magnitude |F| = 32 N. w = 10 m, h = 16 m, and d = 15 m. Calculate the z component of the torque relative to position A.

    2. Relevant equations
    T = r*F


    3. The attempt at a solution
    Not sure how to start this.
    F1 = F*h*w = 32*16*10?
    F2 = F*h = 32*16?
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 31, 2009 #2

    LowlyPion

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    Re: Torque

    T = r X F

    So you want to figure the force acting at a perpendicular to the point at interest.

    In this case your r X F1 will equal |F1|*h, where h is the distance at which it is acting ⊥ to a line through A.
     
  4. Mar 31, 2009 #3
    Re: Torque

    i tried that, its wrong. it says the z component. would that make a difference?
     
  5. Mar 31, 2009 #4

    LowlyPion

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    Re: Torque

    The resultant of r X F is a z component by the right hand rule for taking a cross product.

    Of course you still need to sum up all the other torques from the other forces.
     
  6. Mar 31, 2009 #5
    Re: Torque

    it asks just for the torque for each force that is applied, i.e. F1, F2, F3, ect. After that, it asks for the net torque. for F1 i tried F*h and it was wrong. Would it be F*h*w, since the tail starts at w?
     
  7. Mar 31, 2009 #6

    LowlyPion

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    Re: Torque

    Sorry I thought you were supposed to be determining the sum.

    The |T| is F1*h. But because it is the cross product of y X x, that yields a clockwise torque that is -z

    So for F1 you have the z component is -|F1*h|z

    Counterclockwise torques are positive. Clockwise are negative.
    http://en.wikipedia.org/wiki/Right-hand_rule
     
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