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Find angle with pith ball and vertical wall

  1. Jan 27, 2014 #1
    1. The Question:
    A 10.0 g pith ball, carrying a charge of 1.52 μC hangs from a thread attached to a charged vertical wall carrying a surface charge density σ = 3.57 μC/m2. Find the angle that the thread makes with the vertical.



    2. Relevant equations



    3. My attempt:

    Tcosθ=mg Tsinθ=F
    Canceling tension (sinθ/cosθ)=tanθ=(F/mg)
    F=mgtanθ
    σ=2ε0E
    E=σ/2ε0=201694.9153
    F=EQ=(201694.9153)(1.52E-6)=0.3065762712

    F/mg= 0.0031283293 = tanθ
    tan-1(0.0031283293) = 0.17924

    Is this the correct angle?
     
  2. jcsd
  3. Jan 27, 2014 #2

    gneill

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    Staff: Mentor



    Check your calculation of F/mg. The resulting value looks too small. Did you perhaps forget to change grams into kg for the mass?
     
  4. Jan 27, 2014 #3

    lightgrav

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    Homework Helper

    what are you using for Fgrav? (check the mass units!)
     
  5. Jan 27, 2014 #4
    when i changed g to kg i got the angle to be 72.3
     
  6. Jan 27, 2014 #5

    gneill

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    Staff: Mentor

    Yup. That looks better :smile:
     
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