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Torque & Rotational Motion Question

  1. Oct 22, 2006 #1
    Ok, heres a problem on a quiz that i just cant figure out. I'm having trouble drawing it in the first place:
    At the moment before a diver jumps from a diving board, a force of 1.200 X 10^3 N is exerted on teh diver at an angle of 90 degrees to the board. This force produces a torque in the clockwise direction. At the same time, the diver's weight produces a torque in the counterclockwise direction. The diver's mass is 60 kg, and the angle between the diver's weight and the board is 87.7 degrees. If the net torque acting on the diver is 2985 N*m clockwise, what is the length of the diving board?

    For the first part, doesnt my teacher mean NEGATIVE 2985 N because its in the clockwise direction?
    Anyways, heres the info i got out of that:

    Tnet = 2985 N*m
    F1 = 1200 N
    F2 = ?
    Degrees1 = 90
    Degrees2 = 87.7

    Any ideas about what equations i could use for this, or what it even looks like?!
  2. jcsd
  3. Oct 22, 2006 #2

    Still need help :frown:
  4. Oct 22, 2006 #3


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    Are you sure you have stated the problem correctly? I can't draw it either. A force exerted on the diver can only produce a torque on the diver. Is the first stated force on the diver a force exerted by the board, or is it the total force acting on the diver? The divers weight acts on the diver and can only produce a torque on the diver. Torque is always in reference to some point of rotation. What point are we to use? The logical point is the diver's CM, in which case the weight produces no torque, so all of the torque is due to the first force, a force that can never be found unless we know the distance between the line of the force and the point of rotation. Even if we could find this force, torques applied to the diver have absolutely nothing to do with the length of the board. As stated, I am afraid this is nonsense.
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