1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electric forces

  1. Sep 3, 2008 #1
    1. The problem statement, all variables and given/known data

    Two small metallic spheres, each of mass
    0.14 g are suspended as pendulums by light
    strings from a common point as shown. The
    spheres are given the same electric charge, and
    it is found that the two come to equilibrium
    when each string is at an angle of 7◦ with the
    vertical.
    The value of Coulomb’s constant is
    8.98755 × 109 N · m2/C2 and the acceleration
    of gravity is 9.81 m/s2 .
    If each string is 13.7 cm long, find the mag-
    nitude of the charge on each sphere.
    Answer in units of nC.


    2. Relevant equations


    y=Tcos(theta)=mg
    x=Tsin(theta)=Fe

    3. The attempt at a solution

    Tcos(7)=(.14g)(9.81)
    T=1.38371

    1.38371sin(7)=.168632

    q=sqrt((.1683632)(2*(.137sin7)^2))/8.98755x10^9
    q=1.44639e-7
     
  2. jcsd
  3. Sep 3, 2008 #2

    LowlyPion

    User Avatar
    Homework Helper



    Your method looks fine.

    I haven't checked the math.
    Have you been careful to make sure that the units of grams and cm's is properly matched to the units of g and Coulomb's constant?

    Your answer needs to be in nC.
     
  4. Sep 3, 2008 #3
    I changed it no nC and that is 1.44641e2 nC. It's still not right. :(
     
  5. Sep 3, 2008 #4
    sorry i meant *to
     
  6. Sep 3, 2008 #5

    LowlyPion

    User Avatar
    Homework Helper

    You need to square the total distance between the charges.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Electric forces
  1. Electric Force (Replies: 5)

  2. Electric Forces (Replies: 5)

  3. Electric Forces (Replies: 3)

  4. Electric force (Replies: 5)

  5. Electric Force (Replies: 13)

Loading...