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Calculating torque

  1. Nov 2, 2008 #1
    Calculate the net torque about point for the two forces applied as in the figure below

    The rod and both forces are in the plane of the page.

    torque= ? Nm

    http://session.masteringphysics.com/problemAsset/1026433/5/yg.10.42.jpg

    is the answer -28 Nm?

    i really need help im not sure how to do problems with two forces
     
  2. jcsd
  3. Nov 3, 2008 #2
    Remember:

    [tex]\tau=rF_t=r_{\bot}F=rFsin\theta[/tex]

    So you have to resolve F2 into it's vertical and horizontal components for a start, then calculate the net torque and work from there.
     
    Last edited: Nov 3, 2008
  4. Nov 3, 2008 #3
    can you walk me through it?
    ok how i think you do it is

    12N*2m*sin30
    -8N*5m
    then add the two

    sorry im really not good at this
     
  5. Nov 3, 2008 #4
    Please don't apologise, we all know what it's like :smile:

    Also, I've corrected it now, but I made a mistake in my initial post, you should calculate the torques due to both forces and then the net torque (not force like I initially mentioned, sorry about that slip).

    I also notice that I edited my equation for torque, but that it never changed the equation so I'll say it again.

    [tex]\tau=rF_t=r_{\bot}F=rFsin\theta[/tex]

    Torque can be calculated as any of the following:

    In other words the torque due to [tex]F_2[/tex] can be calculated using:

    [tex]\tau_2=rFsin\theta[/tex]

    and for [tex]F_1[/tex]

    [tex]\tau_1=rF_t[/tex]

    Finally, torque is positive when counterclockwise and negative when clockwise.

    That should sort you out :wink:

    Try again and let us know how far you got ok?
     
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