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Homework Help: Electrical force look for my mistake please

  1. Feb 24, 2010 #1
    A small 5.48 g plastic ball is suspended by a
    24.7 cm long string in a uniform electric field
    of 3980 N/C, as shown.The acceleration of gravity is 9.8 m/s2 , and
    the Coulomb constant is 8.99×109 N · m2/C2..
    If the ball is in equilibrium when the string
    makes a 27.6◦ angle with the vertical as indi-
    cated, what is the net charge on the ball?
    Answer in units of μC.

    This is how i did it.

    q= m*g*tanz/e
    q= 24.7e-3 * 9.81*tan 24.7 / 3980
    q= 31.79545474

    Please tell me what is wrong or if i am using the wrong formula
  2. jcsd
  3. Feb 24, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi Number1! :smile:

    (have a degree: º and try using the X2 tag just above the Reply box :wink:)
    (I haven't checked the rest of your calculation, but …) that 24.7º should be 27.6º. :smile:
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