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HELP with Charges

  1. Jan 23, 2012 #1
    1. The problem statement, all variables and given/known data
    What is the electric force between a glass ball that has +2.8 µC of charge and a rubber ball that has -4.8 µC of charge when they are separated by a distance of 4.5 cm?


    2. Relevant equations

    F=k*Q1*Q2/r^2

    3. The attempt at a solution
    -59.6507
    -8.8888888.889
    4.4380e12
     
  2. jcsd
  3. Jan 23, 2012 #2
    is K 9*10^9
     
  4. Jan 23, 2012 #3
    Yes.
     
  5. Jan 23, 2012 #4
    i got -59.7333 but it is still wrong i do not know what i am doing wrong
     
  6. Jan 23, 2012 #5

    Redbelly98

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    Please show your work.
     
  7. Jan 23, 2012 #6
    (9*10^9)*(2.8*10^(-6))*(-4.8*10^(-6))/0.045^2
     
  8. Jan 23, 2012 #7
    Are you using UTexas Quest? If so, does it give you a value for k? The rounding difference might make your answer a bit off.
     
  9. Jan 23, 2012 #8

    Redbelly98

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    Usually they just want the magnitude of the force for this type of question. Try without the minus sign, otherwise it looks good to me. You should probably not go more precise than 3 significant figures too.
     
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