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Homework Help: Coulomb's Laws-> Please help

  1. Nov 7, 2005 #1
    Coulomb's Laws--> Please help!!!!

    1. Object A is metallic and electrically neutral. It is charged by induction so that it acquires a charge of -2.9 x 10-6 C. Object B is identical to object A and is also electrically neutral. It is charged by induction so that it acquires a charge of +2.4 x 10-6 C. Find the difference in mass between the charged objects.

    Na=(-2.9*10^-6)/(1.602*10^-19)=-1.81*10^13
    Nb=(2.4*10^-6)/(1.602*10^-19)=1.49*10^13

    (Nb-Na)(Mass of electron)=3.7*10^-18
    what did i do wrong?

    2. In a vacuum, two particles have charges of q1 and q2, where q1 = +3.6 uC. They are separated by a distance of 0.36 m, and particle 1 experiences an attractive force of 4.2 N. What is the value of q2, with its sign?

    i used the equatioin F=[k(q1)(q2)]/r^2
    I changed uC to C--> 3.6*10^-6 C
    meters to km
    F=4.2
    i plugged in the knows and solved for q2 and got 1001.3 C.
    please help!

    thanks in advance!
     
  2. jcsd
  3. Nov 7, 2005 #2

    Andrew Mason

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    Homework Helper

    I get: 3.3e13 x 9.1e(-31) = 3.0e(-17) kg
    You should show your numbers. It is difficult to figure out what you did wrong otherwise.

    [tex]q2 = Fr^2/kq1 = 4.2*.13/9e9 * 3.6e(-6) = 17\mu C[/tex]

    AM
     
  4. Nov 8, 2005 #3

    andrevdh

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    Homework Helper

    Problem 1
    Mass of A:
    [tex]m+\delta m_a[/tex]
    Mass of B:
    [tex]m-\delta m_b[/tex]
    Difference in mass:
    [tex]m_A - m_B[/tex]
    [tex](m+\delta m_a)-(m-\delta m_b)[/tex]
    Therefore difference is
    [tex]\delta m_a+\delta m_b[/tex]
     
  5. Nov 8, 2005 #4
    thanks for the help :)
     
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