1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Electrostatic force and # of elementary particles

  1. Mar 28, 2007 #1
    I need to find the electrostatic force & the number of elementary particles between two charged balloons held in the center of their strings (Think of an Isosceles Triangle).

    1. The problem statement, all variables and given/known data
    Mpurple(balloon) - .00354 kg
    Mred - .00405 kg
    Lpurple - .725 m
    Lred - .68 m
    θ = 16°
    T = Tension

    2. Relevant equations & The attempt at a solution

    Fnet1 = Mpurple*g - Tcosθ = 0 T2 = (Mred*g)/cosθ
    Tcosθ = Mpurple*g
    T1 = (Mpurple*g)/cosθ

    Fnetx = F-Tsinθ
    Tsinθ = F
    (M*g)/cosθ * sinθ = F
    M*g*tanθ = (k*q²)/r²
    M*g*tanθ = (k*q²)/(Lpurple*sinθ + Lred*sinθ)
    (Lpurple*sinθ + Lred*sinθ)*( M*g*tanθ) = k*q²
    q² = ((Lpurple*sinθ + Lred*sinθ)*( M*g*tanθ))/k
    q = √(((Lpurple*sinθ + Lred*sinθ)*( M*g*tanθ))/k)
    qPurple = √(((.725*sin16° + .68*sin16°)*( .00354*9.81*tan16°))/8.99x109)
    qRed = √(((.725*sin16° + .68*sin16°)*( .00405*9.81*tan16°))/8.99x109)

    Tpurple = (.00354 kg * 9.81m/s²)/cos16° = 0.036 N
    Tred = (.00405 kg * 9.81m/s²)/cos16° = 0.041 N
    qPurple = 6.54 x 10-7 C
    qRed = 7.01 x 10-7 C

    I don't know how I'd go about finding the Electrostatic force or the number of elementary particles. Any help is appreciated.
  2. jcsd
  3. Mar 28, 2007 #2
    anyway you can post a diagram--or at least better describe the physical situation. You've done a lot of work and we would like to help..
  4. Mar 29, 2007 #3
    OK, diagram coming up (If you can read my handwriting) Also, I misread the handout. I was looking for the number of elementary charges, not particles. I know how to do that, so I only need help with the electrostatic force.

  5. Mar 29, 2007 #4


    User Avatar

    For electrostatic force, use the equation:


    where e0 is the permittivity of free space.

    and r is the distance between the charges. Just find the distance between the balloons (which can be solved with some elementary trig) and you have your answer.
  6. Mar 29, 2007 #5
    Ok, thanks.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook