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Homework Help: Does this problem make sense to anyone?

  1. Aug 10, 2011 #1
    1. The problem statement, all variables and given/known data

    Uniform rod 200cm in legth is in equilibrium. An upward force of 200 dynes is applied 15 cm from the right edge. If the rod is 50dynes. At what pint will rod rotate about?

    3. The attempt at a solution Just one of many

    = 213.33 ?????

    What am I missing? Please I need help.
  2. jcsd
  3. Aug 10, 2011 #2
    Hi there! This sounds like a rotational equilibrium problem! Below is my rationale -

    1) Set a horizontal axis zero point at the left end-point of the rod. Therefore, we have the center of gravity of the rod at 100cm, and we have the point of upward force at 185cm.

    2) Set the point of rotation at location X, (i.e. X cm from the left end-point).

    3) Given the system is at equilibrium, therefore the torque moving the rod at clock-wise direction (produced by upward lift force at 185cm), equals to the torque moving the rod at counter-clock-wise direction (weight of the rod, at the center of gravity, at 100cm). This is the foundation for setting the equation to solve for X.

    4) Setting equations: Torque CW = Torque CCW
    => 50*(X-100)=200*(185-X)
    => X=168cm
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