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Acceleration of 2 charges

  1. Sep 17, 2009 #1
    1. The problem statement, all variables and given/known data

    Two very small 8.55-g spheres, 20.0cm apart from center to center, are charged by adding equal numbers of electrons to each of them.

    Disregarding all other forces, how many electrons would you have to add to each sphere so that the two spheres will accelerate at 15.0 g when released?

    2. Relevant equations

    F=ma
    F=k(q1q2/r^2)
    q=ne



    3. The attempt at a solution

    for one.. i don't know why the acceleration is at 15.0 g?

    But i did try to set the forces equal and solve q, then plugged q in to the equation q=ne and it wasn't right.

    Please help
     
  2. jcsd
  3. Sep 17, 2009 #2

    rl.bhat

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    Show your calculations.
     
  4. Sep 17, 2009 #3
    F=ma=F=k(q1q2/r^2)

    q1=q2; let Q^2=q1q2

    sqrt(mar^2/k)=Q

    sqrt((8.55g*15.0m/s)((2m)^2)/k)=Q

    Q=2.39e-4

    Q=ne

    n=2.39e-4/1.6e-19

    =1.49e15 electrons
     
  5. Sep 17, 2009 #4

    rl.bhat

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    The acceleration is 15*g i.e. 15*9.8 m/s^2
    In the solution you have written (2m)^2. What is that?
     
  6. Sep 17, 2009 #5
    they are 20cm apart? so .2m
     
  7. Sep 17, 2009 #6
    i messed up and wrote 2m. so 15g is 15x the acceleration of gravity
     
  8. Sep 17, 2009 #7

    rl.bhat

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