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Homework Help: Tension (related to Fe) Question and Gauss Question

  1. Jul 18, 2006 #1
    I have two questions

    Regarding tension:
    Two balls are suspended as a pendulum from a shared point. The balls are held at angle theta (due to electric force). I understand that I am supposed to add the forces of the tension, the electric force and the force due to gravity, and that they should total zero, but for some reason I'm having issues with solving for tension. Should I be finding x component and y component of T and find a resultant T to then add to Fg and Fe? Or should I add the x components of Fg and Fe and Ft and then the y components of the same and then find resultant force? I'm solving for T so I can find Fe, which I'll then use to find q. The mass of the balls are the same.

    Regarding Gauss:
    My textbook offers no insight into how to compute electrical fields for concentric shell and sphere, and I can't seem to find much through internet searches. Wondering if someone could help explain how to solve for such a thing.
  2. jcsd
  3. Jul 18, 2006 #2


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    For the tension... if you know the angle, you should also be able to calculate the vertical component (what's holding the balls up?). Then you can calculate the total tension.

    If you don't know the angle, keep in mind that two forces are acting on the ball (that the tension is opposing): electric and gravitational. They should form a vector directly opposite the direction of the tension force

    For Gauss:

    Draw a sphere around your spherical charge. You know Integral(EdA)=q/e (e is epsilon). E is constant, and the surface area of a sphere is 4*pi*r^2
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